1OKSH(1)                   BSD General Commands Manual                  OKSH(1)


4     oksh, rksh — public domain Korn shell


7     oksh [-+abCefhiklmnpruvXx] [-+o option]
8          [-c string | -s | file [argument ...]]


11     oksh is a command interpreter intended for both interactive and shell
12     script use.  Its command language is a superset of the sh(1) shell lan‐
13     guage.
15     The options are as follows:
17     -c string
18             oksh will execute the command(s) contained in string.
20     -i      Interactive shell.  A shell is “interactive” if this option is
21             used or if both standard input and standard error are attached to
22             a tty(4).  An interactive shell has job control enabled, ignores
23             the SIGINT, SIGQUIT, and SIGTERM signals, and prints prompts be‐
24             fore reading input (see the PS1 and PS2 parameters).  For non-in‐
25             teractive shells, the trackall option is on by default (see the
26             set command below).
28     -l      Login shell.  If the basename the shell is called with (i.e.
29             argv[0]) starts with ‘-’ or if this option is used, the shell is
30             assumed to be a login shell and the shell reads and executes the
31             contents of /etc/profile and $HOME/.profile if they exist and are
32             readable.
34     -p      Privileged shell.  A shell is “privileged” if this option is used
35             or if the real user ID or group ID does not match the effective
36             user ID or group ID (see getuid(2) and getgid(2)).  A privileged
37             shell does not process $HOME/.profile nor the ENV parameter (see
38             below).  Instead, the file /etc/suid_profile is processed.
39             Clearing the privileged option causes the shell to set its effec‐
40             tive user ID (group ID) to its real user ID (group ID).
42     -r      Restricted shell.  A shell is “restricted” if this option is
43             used; if the basename the shell was invoked with was “rksh”; or
44             if the SHELL parameter is set to “rksh”.  The following restric‐
45             tions come into effect after the shell processes any profile and
46             ENV files:
48             The cd command is disabled.
49             The SHELL, ENV, and PATH parameters cannot be changed.
50             Command names can't be specified with absolute or relative
51                 paths.
52             The -p option of the built-in command command can't be used.
53             Redirections that create files can't be used (i.e. ‘>’, ‘>|’,
54>>’, ‘<>’).
56     -s      The shell reads commands from standard input; all non-option ar‐
57             guments are positional parameters.
59     In addition to the above, the options described in the set built-in com‐
60     mand can also be used on the command line: both [-+abCefhkmnuvXx] and
61     [-+o option] can be used for single letter or long options, respectively.
63     If neither the -c nor the -s option is specified, the first non-option
64     argument specifies the name of a file the shell reads commands from.  If
65     there are no non-option arguments, the shell reads commands from the
66     standard input.  The name of the shell (i.e. the contents of $0) is de‐
67     termined as follows: if the -c option is used and there is a non-option
68     argument, it is used as the name; if commands are being read from a file,
69     the file is used as the name; otherwise, the basename the shell was
70     called with (i.e. argv[0]) is used.
72     If the ENV parameter is set when an interactive shell starts (or, in the
73     case of login shells, after any profiles are processed), its value is
74     subjected to parameter, command, arithmetic, and tilde (‘~’) substitution
75     and the resulting file (if any) is read and executed.  In order to have
76     an interactive (as opposed to login) shell process a startup file, ENV
77     may be set and exported (see below) in $HOME/.profile - future interac‐
78     tive shell invocations will process any file pointed to by $ENV:
80           export ENV=$HOME/.kshrc
82     $HOME/.kshrc is then free to specify instructions for interactive shells.
83     For example, the global configuration file may be sourced:
85           . /etc/ksh.kshrc
87     The above strategy may be employed to keep setup procedures for login
88     shells in $HOME/.profile and setup procedures for interactive shells in
89     $HOME/.kshrc.  Of course, since login shells are also interactive, any
90     commands placed in $HOME/.kshrc will be executed by login shells too.
92     The exit status of the shell is 127 if the command file specified on the
93     command line could not be opened, or non-zero if a fatal syntax error oc‐
94     curred during the execution of a script.  In the absence of fatal errors,
95     the exit status is that of the last command executed, or zero, if no com‐
96     mand is executed.
98   Command syntax
99     The shell begins parsing its input by breaking it into words.  Words,
100     which are sequences of characters, are delimited by unquoted whitespace
101     characters (space, tab, and newline) or meta-characters (‘<’, ‘>’, ‘|’,
102     ‘;’, ‘(’, ‘)’, and ‘&’).  Aside from delimiting words, spaces and tabs
103     are ignored, while newlines usually delimit commands.  The meta-charac‐
104     ters are used in building the following tokens: ‘<’, ‘<&’, ‘<<’, ‘>’,
105>&’, ‘>>’, etc. are used to specify redirections (see Input/output
106     redirection below); ‘|’ is used to create pipelines; ‘|&’ is used to cre‐
107     ate co-processes (see Co-processes below); ‘;’ is used to separate com‐
108     mands; ‘&’ is used to create asynchronous pipelines; ‘&&’ and ‘||’ are
109     used to specify conditional execution; ‘;;’ is used in case statements;
110     ‘(( .. ))’ is used in arithmetic expressions; and lastly, ‘( .. )’ is
111     used to create subshells.
113     Whitespace and meta-characters can be quoted individually using a back‐
114     slash (‘\’), or in groups using double (‘"’) or single (‘'’) quotes.  The
115     following characters are also treated specially by the shell and must be
116     quoted if they are to represent themselves: ‘\’, ‘"’, ‘'’, ‘#’, ‘$’, ‘`’,
117     ‘~’, ‘{’, ‘}’, ‘*’, ‘?’, and ‘[’.  The first three of these are the above
118     mentioned quoting characters (see Quoting below); ‘#’, if used at the be‐
119     ginning of a word, introduces a comment — everything after the ‘#’ up to
120     the nearest newline is ignored; ‘$’ is used to introduce parameter, com‐
121     mand, and arithmetic substitutions (see Substitution below); ‘`’ intro‐
122     duces an old-style command substitution (see Substitution below); ‘~’ be‐
123     gins a directory expansion (see Tilde expansion below); ‘{’ and ‘}’ de‐
124     limit csh(1)-style alternations (see Brace expansion below); and finally,
125     ‘*’, ‘?’, and ‘[’ are used in file name generation (see File name
126     patterns below).
128     As words and tokens are parsed, the shell builds commands, of which there
129     are two basic types: simple-commands, typically programs that are exe‐
130     cuted, and compound-commands, such as for and if statements, grouping
131     constructs, and function definitions.
133     A simple-command consists of some combination of parameter assignments
134     (see Parameters below), input/output redirections (see Input/output
135     redirections below), and command words; the only restriction is that pa‐
136     rameter assignments come before any command words.  The command words, if
137     any, define the command that is to be executed and its arguments.  The
138     command may be a shell built-in command, a function, or an external com‐
139     mand (i.e. a separate executable file that is located using the PATH pa‐
140     rameter; see Command execution below).
142     All command constructs have an exit status.  For external commands, this
143     is related to the status returned by wait(2) (if the command could not be
144     found, the exit status is 127; if it could not be executed, the exit sta‐
145     tus is 126).  The exit status of other command constructs (built-in com‐
146     mands, functions, compound-commands, pipelines, lists, etc.) are all
147     well-defined and are described where the construct is described.  The
148     exit status of a command consisting only of parameter assignments is that
149     of the last command substitution performed during the parameter assign‐
150     ment or 0 if there were no command substitutions.
152     Commands can be chained together using the ‘|’ token to form pipelines,
153     in which the standard output of each command but the last is piped (see
154     pipe(2)) to the standard input of the following command.  The exit status
155     of a pipeline is that of its last command.  A pipeline may be prefixed by
156     the ‘!’ reserved word, which causes the exit status of the pipeline to be
157     logically complemented: if the original status was 0, the complemented
158     status will be 1; if the original status was not 0, the complemented sta‐
159     tus will be 0.
161     Lists of commands can be created by separating pipelines by any of the
162     following tokens: ‘&&’, ‘||’, ‘&’, ‘|&’, and ‘;’.  The first two are for
163     conditional execution: “cmd1 && cmd2” executes cmd2 only if the exit sta‐
164     tus of cmd1 is zero; ‘||’ is the opposite — cmd2 is executed only if the
165     exit status of cmd1 is non-zero.  ‘&&’ and ‘||’ have equal precedence
166     which is higher than that of ‘&’, ‘|&’, and ‘;’, which also have equal
167     precedence.  The ‘&&’ and ‘||’ operators are "left-associative".  For ex‐
168     ample, both of these commands will print only "bar":
170           $ false && echo foo || echo bar
171           $ true || echo foo && echo bar
173     The ‘&’ token causes the preceding command to be executed asynchronously;
174     that is, the shell starts the command but does not wait for it to com‐
175     plete (the shell does keep track of the status of asynchronous commands;
176     see Job control below).  When an asynchronous command is started when job
177     control is disabled (i.e. in most scripts), the command is started with
178     signals SIGINT and SIGQUIT ignored and with input redirected from
179     /dev/null (however, redirections specified in the asynchronous command
180     have precedence).  The ‘|&’ operator starts a co-process which is a spe‐
181     cial kind of asynchronous process (see Co-processes below).  A command
182     must follow the ‘&&’ and ‘||’ operators, while it need not follow ‘&’,
183     ‘|&’, or ‘;’.  The exit status of a list is that of the last command exe‐
184     cuted, with the exception of asynchronous lists, for which the exit sta‐
185     tus is 0.
187     Compound commands are created using the following reserved words.  These
188     words are only recognized if they are unquoted and if they are used as
189     the first word of a command (i.e. they can't be preceded by parameter as‐
190     signments or redirections):
192           case   esac       in       until   ((   }
193           do     fi         name     while   ))
194           done   for        select   !       [[
195           elif   function   then     (       ]]
196           else   if         time     )       {
198     Note: Some shells (but not this one) execute control structure commands
199     in a subshell when one or more of their file descriptors are redirected,
200     so any environment changes inside them may fail.  To be portable, the
201     exec statement should be used instead to redirect file descriptors before
202     the control structure.
204     In the following compound command descriptions, command lists (denoted as
205     list) that are followed by reserved words must end with a semicolon, a
206     newline, or a (syntactically correct) reserved word.  For example, the
207     following are all valid:
209           $ { echo foo; echo bar; }
210           $ { echo foo; echo bar<newline> }
211           $ { { echo foo; echo bar; } }
213     This is not valid:
215           $ { echo foo; echo bar }
217     (list)  Execute list in a subshell.  There is no implicit way to pass en‐
218             vironment changes from a subshell back to its parent.
220     { list; }
221             Compound construct; list is executed, but not in a subshell.
222             Note that ‘{’ and ‘}’ are reserved words, not meta-characters.
224     case word in [[(] pattern [| pattern] ...) list ;; ] ... esac
225             The case statement attempts to match word against a specified
226             pattern; the list associated with the first successfully matched
227             pattern is executed.  Patterns used in case statements are the
228             same as those used for file name patterns except that the re‐
229             strictions regarding ‘.’ and ‘/’ are dropped.  Note that any un‐
230             quoted space before and after a pattern is stripped; any space
231             within a pattern must be quoted.  Both the word and the patterns
232             are subject to parameter, command, and arithmetic substitution,
233             as well as tilde substitution.  For historical reasons, open and
234             close braces may be used instead of in and esac e.g. case $foo {
235             *) echo bar; }.  The exit status of a case statement is that of
236             the executed list; if no list is executed, the exit status is
237             zero.
239     for name [in [word ...]]; do list; done
240             For each word in the specified word list, the parameter name is
241             set to the word and list is executed.  If in is not used to spec‐
242             ify a word list, the positional parameters ($1, $2, etc.) are
243             used instead.  For historical reasons, open and close braces may
244             be used instead of do and done e.g. for i; { echo $i; }.  The
245             exit status of a for statement is the last exit status of list.
246             If there are no items, list is not executed and the exit status
247             is zero.
249     if list; then list; [elif list; then list;] ... [else list;] fi
250             If the exit status of the first list is zero, the second list is
251             executed; otherwise, the list following the elif, if any, is exe‐
252             cuted with similar consequences.  If all the lists following the
253             if and elifs fail (i.e. exit with non-zero status), the list fol‐
254             lowing the else is executed.  The exit status of an if statement
255             is that of non-conditional list that is executed; if no non-con‐
256             ditional list is executed, the exit status is zero.
258     select name [in word ...]; do list; done
259             The select statement provides an automatic method of presenting
260             the user with a menu and selecting from it.  An enumerated list
261             of the specified word(s) is printed on standard error, followed
262             by a prompt (PS3: normally ‘#? ’).  A number corresponding to one
263             of the enumerated words is then read from standard input, name is
264             set to the selected word (or unset if the selection is not
265             valid), REPLY is set to what was read (leading/trailing space is
266             stripped), and list is executed.  If a blank line (i.e. zero or
267             more IFS characters) is entered, the menu is reprinted without
268             executing list.
270             When list completes, the enumerated list is printed if REPLY is
271             NULL, the prompt is printed, and so on.  This process continues
272             until an end-of-file is read, an interrupt is received, or a
273             break statement is executed inside the loop.  If “in word ...” is
274             omitted, the positional parameters are used (i.e. $1, $2, etc.).
275             For historical reasons, open and close braces may be used instead
276             of do and done e.g. select i; { echo $i; }.  The exit status of a
277             select statement is zero if a break statement is used to exit the
278             loop, non-zero otherwise.
280     until list; do list; done
281             This works like while, except that the body is executed only
282             while the exit status of the first list is non-zero.
284     while list; do list; done
285             A while is a pre-checked loop.  Its body is executed as often as
286             the exit status of the first list is zero.  The exit status of a
287             while statement is the last exit status of the list in the body
288             of the loop; if the body is not executed, the exit status is
289             zero.
291     function name { list; }
292             Defines the function name (see Functions below).  Note that redi‐
293             rections specified after a function definition are performed
294             whenever the function is executed, not when the function defini‐
295             tion is executed.
297     name() command
298             Mostly the same as function (see Functions below).
300     time [-p] [pipeline]
301             The time reserved word is described in the Command execution sec‐
302             tion.
304     (( expression ))
305             The arithmetic expression expression is evaluated; equivalent to
306             let expression (see Arithmetic expressions and the let command,
307             below).
309     [[ expression ]]
310             Similar to the test and [ ... ] commands (described later), with
311             the following exceptions:
313                   Field splitting and file name generation are not per‐
314                       formed on arguments.
316                   The -a (AND) and -o (OR) operators are replaced with
317                       ‘&&’ and ‘||’, respectively.
319                   Operators (e.g. ‘-f’, ‘=’, ‘!’) must be unquoted.
321                   The second operand of the ‘!=’ and ‘=’ expressions are
322                       patterns (e.g. the comparison [[ foobar = f*r ]] suc‐
323                       ceeds).
325                   There are two additional binary operators, ‘<’ and ‘>’,
326                       which return true if their first string operand is less
327                       than, or greater than, their second string operand, re‐
328                       spectively.
330                   The single argument form of test, which tests if the
331                       argument has a non-zero length, is not valid; explicit
332                       operators must always be used e.g. instead of [ str ]
333                       use [[ -n str ]].
335                   Parameter, command, and arithmetic substitutions are
336                       performed as expressions are evaluated and lazy expres‐
337                       sion evaluation is used for the ‘&&’ and ‘||’ opera‐
338                       tors.  This means that in the following statement, $(<
339                       foo) is evaluated if and only if the file foo exists
340                       and is readable:
342                             $ [[ -r foo && $(< foo) = b*r ]]
344   Quoting
345     Quoting is used to prevent the shell from treating characters or words
346     specially.  There are three methods of quoting.  First, ‘\’ quotes the
347     following character, unless it is at the end of a line, in which case
348     both the ‘\’ and the newline are stripped.  Second, a single quote (‘'’)
349     quotes everything up to the next single quote (this may span lines).
350     Third, a double quote (‘"’) quotes all characters, except ‘$’, ‘`’ and
351     ‘\’, up to the next unquoted double quote.  ‘$’ and ‘`’ inside double
352     quotes have their usual meaning (i.e. parameter, command, or arithmetic
353     substitution) except no field splitting is carried out on the results of
354     double-quoted substitutions.  If a ‘\’ inside a double-quoted string is
355     followed by ‘\’, ‘$’, ‘`’, or ‘"’, it is replaced by the second charac‐
356     ter; if it is followed by a newline, both the ‘\’ and the newline are
357     stripped; otherwise, both the ‘\’ and the character following are un‐
358     changed.
360   Aliases
361     There are two types of aliases: normal command aliases and tracked
362     aliases.  Command aliases are normally used as a short hand for a long or
363     often used command.  The shell expands command aliases (i.e. substitutes
364     the alias name for its value) when it reads the first word of a command.
365     An expanded alias is re-processed to check for more aliases.  If a com‐
366     mand alias ends in a space or tab, the following word is also checked for
367     alias expansion.  The alias expansion process stops when a word that is
368     not an alias is found, when a quoted word is found, or when an alias word
369     that is currently being expanded is found.
371     The following command aliases are defined automatically by the shell:
373           autoload='typeset -fu'
374           functions='typeset -f'
375           hash='alias -t'
376           history='fc -l'
377           integer='typeset -i'
378           local='typeset'
379           login='exec login'
380           nohup='nohup '
381           r='fc -s'
382           stop='kill -STOP'
384     Tracked aliases allow the shell to remember where it found a particular
385     command.  The first time the shell does a path search for a command that
386     is marked as a tracked alias, it saves the full path of the command.  The
387     next time the command is executed, the shell checks the saved path to see
388     that it is still valid, and if so, avoids repeating the path search.
389     Tracked aliases can be listed and created using alias -t.  Note that
390     changing the PATH parameter clears the saved paths for all tracked
391     aliases.  If the trackall option is set (i.e. set -o trackall or set -h),
392     the shell tracks all commands.  This option is set automatically for non-
393     interactive shells.  For interactive shells, only the following commands
394     are automatically tracked: cat(1), cc(1), chmod(1), cp(1), date(1),
395     ed(1), emacs, grep(1), ls(1), mail(1), make(1), mv(1), pr(1), rm(1),
396     sed(1), sh(1), vi(1), and who(1).
398   Substitution
399     The first step the shell takes in executing a simple-command is to per‐
400     form substitutions on the words of the command.  There are three kinds of
401     substitution: parameter, command, and arithmetic.  Parameter substitu‐
402     tions, which are described in detail in the next section, take the form
403     $name or ${...}; command substitutions take the form $(command) or
404     `command`; and arithmetic substitutions take the form $((expression)).
406     If a substitution appears outside of double quotes, the results of the
407     substitution are generally subject to word or field splitting according
408     to the current value of the IFS parameter.  The IFS parameter specifies a
409     list of characters which are used to break a string up into several
410     words; any characters from the set space, tab, and newline that appear in
411     the IFS characters are called “IFS whitespace”.  Sequences of one or more
412     IFS whitespace characters, in combination with zero or one non-IFS white‐
413     space characters, delimit a field.  As a special case, leading and trail‐
414     ing IFS whitespace is stripped (i.e. no leading or trailing empty field
415     is created by it); leading non-IFS whitespace does create an empty field.
417     Example: If IFS is set to “<space>:”, and VAR is set to
418     “<space>A<space>:<space><space>B::D”, the substitution for $VAR results
419     in four fields: ‘A’, ‘B’, ‘’ (an empty field), and ‘D’.  Note that if the
420     IFS parameter is set to the NULL string, no field splitting is done; if
421     the parameter is unset, the default value of space, tab, and newline is
422     used.
424     Also, note that the field splitting applies only to the immediate result
425     of the substitution.  Using the previous example, the substitution for
426     $VAR:E results in the fields: ‘A’, ‘B’, ‘’, and ‘D:E’, not ‘A’, ‘B’, ‘’,
427     ‘D’, and ‘E’.  This behavior is POSIX compliant, but incompatible with
428     some other shell implementations which do field splitting on the word
429     which contained the substitution or use IFS as a general whitespace de‐
430     limiter.
432     The results of substitution are, unless otherwise specified, also subject
433     to brace expansion and file name expansion (see the relevant sections be‐
434     low).
436     A command substitution is replaced by the output generated by the speci‐
437     fied command, which is run in a subshell.  For $(command) substitutions,
438     normal quoting rules are used when command is parsed; however, for the
439     `command` form, a ‘\’ followed by any of ‘$’, ‘`’, or ‘\’ is stripped (a
440     ‘\’ followed by any other character is unchanged).  As a special case in
441     command substitutions, a command of the form <file is interpreted to mean
442     substitute the contents of file.  Note that $(< foo) has the same effect
443     as $(cat foo), but it is carried out more efficiently because no process
444     is started.
446     Arithmetic substitutions are replaced by the value of the specified ex‐
447     pression.  For example, the command echo $((2+3*4)) prints 14.  See
448     Arithmetic expressions for a description of an expression.
450   Parameters
451     Parameters are shell variables; they can be assigned values and their
452     values can be accessed using a parameter substitution.  A parameter name
453     is either one of the special single punctuation or digit character param‐
454     eters described below, or a letter followed by zero or more letters or
455     digits (‘_’ counts as a letter).  The latter form can be treated as ar‐
456     rays by appending an array index of the form [expr] where expr is an
457     arithmetic expression.  Parameter substitutions take the form $name,
458     ${name}, or ${name[expr]} where name is a parameter name.  If expr is a
459     literal ‘@’ then the named array is expanded using the same quoting rules
460     as ‘$@’, while if expr is a literal ‘*’ then the named array is expanded
461     using the same quoting rules as ‘$*’.  If substitution is performed on a
462     parameter (or an array parameter element) that is not set, a null string
463     is substituted unless the nounset option (set -o nounset or set -u) is
464     set, in which case an error occurs.
466     Parameters can be assigned values in a number of ways.  First, the shell
467     implicitly sets some parameters like ‘#’, ‘PWD’, and ‘$’; this is the
468     only way the special single character parameters are set.  Second, param‐
469     eters are imported from the shell's environment at startup.  Third, pa‐
470     rameters can be assigned values on the command line: for example, FOO=bar
471     sets the parameter “FOO” to “bar”; multiple parameter assignments can be
472     given on a single command line and they can be followed by a simple-com‐
473     mand, in which case the assignments are in effect only for the duration
474     of the command (such assignments are also exported; see below for the im‐
475     plications of this).  Note that both the parameter name and the ‘=’ must
476     be unquoted for the shell to recognize a parameter assignment.  The
477     fourth way of setting a parameter is with the export, readonly, and
478     typeset commands; see their descriptions in the Command execution sec‐
479     tion.  Fifth, for and select loops set parameters as well as the getopts,
480     read, and set -A commands.  Lastly, parameters can be assigned values us‐
481     ing assignment operators inside arithmetic expressions (see Arithmetic
482     expressions below) or using the ${name=value} form of the parameter sub‐
483     stitution (see below).
485     Parameters with the export attribute (set using the export or typeset -x
486     commands, or by parameter assignments followed by simple commands) are
487     put in the environment (see environ(7)) of commands run by the shell as
488     name=value pairs.  The order in which parameters appear in the environ‐
489     ment of a command is unspecified.  When the shell starts up, it extracts
490     parameters and their values from its environment and automatically sets
491     the export attribute for those parameters.
493     Modifiers can be applied to the ${name} form of parameter substitution:
495     ${name:-word}
496             If name is set and not NULL, it is substituted; otherwise, word
497             is substituted.
499     ${name:+word}
500             If name is set and not NULL, word is substituted; otherwise,
501             nothing is substituted.
503     ${name:=word}
504             If name is set and not NULL, it is substituted; otherwise, it is
505             assigned word and the resulting value of name is substituted.
507     ${name:?word}
508             If name is set and not NULL, it is substituted; otherwise, word
509             is printed on standard error (preceded by name:) and an error oc‐
510             curs (normally causing termination of a shell script, function,
511             or script sourced using the ‘.’ built-in).  If word is omitted,
512             the string “parameter null or not set” is used instead.
514     In the above modifiers, the ‘:’ can be omitted, in which case the condi‐
515     tions only depend on name being set (as opposed to set and not NULL).  If
516     word is needed, parameter, command, arithmetic, and tilde substitution
517     are performed on it; if word is not needed, it is not evaluated.
519     The following forms of parameter substitution can also be used:
521     ${#name}
522             The number of positional parameters if name is ‘*’, ‘@’, or not
523             specified; otherwise the length of the string value of parameter
524             name.
526     ${#name[*]}
527     ${#name[@]}
528             The number of elements in the array name.
530     ${name#pattern}
531     ${name##pattern}
532             If pattern matches the beginning of the value of parameter name,
533             the matched text is deleted from the result of substitution.  A
534             single ‘#’ results in the shortest match, and two of them result
535             in the longest match.
537     ${name%pattern}
538     ${name%%pattern}
539             Like ${..#..} substitution, but it deletes from the end of the
540             value.
542     The following special parameters are implicitly set by the shell and can‐
543     not be set directly using assignments:
545     !        Process ID of the last background process started.  If no back‐
546              ground processes have been started, the parameter is not set.
548     #        The number of positional parameters ($1, $2, etc.).
550     $        The PID of the shell, or the PID of the original shell if it is
551              a subshell.  Do NOT use this mechanism for generating temporary
552              file names; see mktemp(1) instead.
554     -        The concatenation of the current single letter options (see the
555              set command below for a list of options).
557     ?        The exit status of the last non-asynchronous command executed.
558              If the last command was killed by a signal, $? is set to 128
559              plus the signal number.
561     0        The name of the shell, determined as follows: the first argument
562              to oksh if it was invoked with the -c option and arguments were
563              given; otherwise the file argument, if it was supplied; or else
564              the basename the shell was invoked with (i.e. argv[0]).  $0 is
565              also set to the name of the current script or the name of the
566              current function, if it was defined with the function keyword
567              (i.e. a Korn shell style function).
569     1 ... 9  The first nine positional parameters that were supplied to the
570              shell, function, or script sourced using the ‘.’ built-in.  Fur‐
571              ther positional parameters may be accessed using ${number}.
573     *        All positional parameters (except parameter 0) i.e. $1, $2, $3,
574              ...  If used outside of double quotes, parameters are separate
575              words (which are subjected to word splitting); if used within
576              double quotes, parameters are separated by the first character
577              of the IFS parameter (or the empty string if IFS is NULL).
579     @        Same as $*, unless it is used inside double quotes, in which
580              case a separate word is generated for each positional parameter.
581              If there are no positional parameters, no word is generated.  $@
582              can be used to access arguments, verbatim, without losing NULL
583              arguments or splitting arguments with spaces.
585     The following parameters are set and/or used by the shell:
587     _ (underscore)
588                When an external command is executed by the shell, this param‐
589                eter is set in the environment of the new process to the path
590                of the executed command.  In interactive use, this parameter
591                is also set in the parent shell to the last word of the previ‐
592                ous command.  When MAILPATH messages are evaluated, this pa‐
593                rameter contains the name of the file that changed (see the
594                MAILPATH parameter, below).
596     CDPATH     Search path for the cd built-in command.  It works the same
597                way as PATH for those directories not beginning with ‘/’ or
598                ‘.’ in cd commands.  Note that if CDPATH is set and does not
599                contain ‘.’ or contains an empty path, the current directory
600                is not searched.  Also, the cd built-in command will display
601                the resulting directory when a match is found in any search
602                path other than the empty path.
604     COLUMNS    Set to the number of columns on the terminal or window.  Cur‐
605                rently set to the “cols” value as reported by stty(1) if that
606                value is non-zero.  This parameter is used by the interactive
607                line editing modes, and by the select, set -o, and kill -l
608                commands to format information columns.
610     EDITOR     If the VISUAL parameter is not set, this parameter controls
611                the command-line editing mode for interactive shells.  See the
612                VISUAL parameter below for how this works.
614                Note: traditionally, EDITOR was used to specify the name of an
615                (old-style) line editor, such as ed(1), and VISUAL was used to
616                specify a (new-style) screen editor, such as vi(1).  Hence if
617                VISUAL is set, it overrides EDITOR.
619     ENV        If this parameter is found to be set after any profile files
620                are executed, the expanded value is used as a shell startup
621                file.  It typically contains function and alias definitions.
623     EXECSHELL  If set, this parameter is assumed to contain the shell that is
624                to be used to execute commands that execve(2) fails to execute
625                and which do not start with a “#!shell” sequence.
627     FCEDIT     The editor used by the fc command (see below).
629     FPATH      Like PATH, but used when an undefined function is executed to
630                locate the file defining the function.  It is also searched
631                when a command can't be found using PATH.  See Functions below
632                for more information.
635                A colon separated list of history settings.  If ignoredups is
636                present, lines identical to the previous history line will not
637                be saved.  If ignorespace is present, lines starting with a
638                space will not be saved.  Unknown settings are ignored.
640     HISTFILE   The name of the file used to store command history.  When as‐
641                signed to, history is loaded from the specified file.  Also,
642                several invocations of the shell running on the same machine
643                will share history if their HISTFILE parameters all point to
644                the same file.
646                Note: If HISTFILE isn't set, no history file is used.  This is
647                different from the original Korn shell, which uses
648                $HOME/.sh_history.
650     HISTSIZE   The number of commands normally stored for history.  The de‐
651                fault is 500.
653     HOME       The default directory for the cd command and the value substi‐
654                tuted for an unqualified ~ (see Tilde expansion below).
656     IFS        Internal field separator, used during substitution and by the
657                read command, to split values into distinct arguments; nor‐
658                mally set to space, tab, and newline.  See Substitution above
659                for details.
661                Note: This parameter is not imported from the environment when
662                the shell is started.
665                The version of the shell and the date the version was created
666                (read-only).
668     LINENO     The line number of the function or shell script that is cur‐
669                rently being executed.
671     LINES      Set to the number of lines on the terminal or window.
673     MAIL       If set, the user will be informed of the arrival of mail in
674                the named file.  This parameter is ignored if the MAILPATH pa‐
675                rameter is set.
677     MAILCHECK  How often, in seconds, the shell will check for mail in the
678                file(s) specified by MAIL or MAILPATH.  If set to 0, the shell
679                checks before each prompt.  The default is 600 (10 minutes).
681     MAILPATH   A list of files to be checked for mail.  The list is colon
682                separated, and each file may be followed by a ‘?’ and a mes‐
683                sage to be printed if new mail has arrived.  Command, parame‐
684                ter, and arithmetic substitution is performed on the message
685                and, during substitution, the parameter $_ contains the name
686                of the file.  The default message is “you have mail in $_”.
688     OLDPWD     The previous working directory.  Unset if cd has not success‐
689                fully changed directories since the shell started, or if the
690                shell doesn't know where it is.
692     OPTARG     When using getopts, it contains the argument for a parsed op‐
693                tion, if it requires one.
695     OPTIND     The index of the next argument to be processed when using
696                getopts.  Assigning 1 to this parameter causes getopts to
697                process arguments from the beginning the next time it is in‐
698                voked.
700     PATH       A colon separated list of directories that are searched when
701                looking for commands and files sourced using the ‘.’ command
702                (see below).  An empty string resulting from a leading or
703                trailing colon, or two adjacent colons, is treated as a ‘.’
704                (the current directory).
707                If set, this parameter causes the posix option to be enabled.
708                See POSIX mode below.
710     PPID       The process ID of the shell's parent (read-only).
712     PS1        The primary prompt for interactive shells.  Parameter, com‐
713                mand, and arithmetic substitutions are performed, and the
714                prompt string can be customised using backslash-escaped spe‐
715                cial characters.
717                Note that since the command-line editors try to figure out how
718                long the prompt is (so they know how far it is to the edge of
719                the screen), escape codes in the prompt tend to mess things
720                up.  You can tell the shell not to count certain sequences
721                (such as escape codes) by using the \[...\] substitution (see
722                below) or by prefixing your prompt with a non-printing charac‐
723                ter (such as control-A) followed by a carriage return and then
724                delimiting the escape codes with this non-printing character.
725                By the way, don't blame me for this hack; it's in the original
726                oksh.
728                The default prompt is the first part of the hostname, followed
729                by ‘$ ’ for non-root users, ‘# ’ for root.
731                The following backslash-escaped special characters can be used
732                to customise the prompt:
734                \a            Insert an ASCII bell character.
735                \d            The current date, in the format “Day Month Date”
736                              for example “Wed Nov 03”.
737                \D{format}    The current date, with format converted by
738                              strftime(3).  The braces must be specified.
739                \e            Insert an ASCII escape character.
740                \h            The hostname, minus domain name.
741                \H            The full hostname, including domain name.
742                \j            Current number of jobs running (see Job control
743                              below).
744                \l            The controlling terminal.
745                \n            Insert a newline character.
746                \r            Insert a carriage return character.
747                \s            The name of the shell.
748                \t            The current time, in 24-hour HH:MM:SS format.
749                \T            The current time, in 12-hour HH:MM:SS format.
750                \@            The current time, in 12-hour HH:MM:SS AM/PM for‐
751                              mat.
752                \A            The current time, in 24-hour HH:MM format.
753                \u            The current user's username.
754                \v            The current version of oksh.
755                \V            Like ‘\v’, but more verbose.
756                \w            The current working directory.  $HOME is abbre‐
757                              viated as ‘~’.
758                \W            The basename of the current working directory.
759                              $HOME is abbreviated as ‘~’.
760                \!            The current history number.  An unescaped ‘!’
761                              will produce the current history number too, as
762                              per the POSIX specification.  A literal ‘!’ can
763                              be put in the prompt by placing ‘!!’ in PS1.
764                \#            The current command number.  This could be dif‐
765                              ferent to the current history number, if
766                              HISTFILE contains a history list from a previous
767                              session.
768                \$            The default prompt character i.e. ‘#’ if the ef‐
769                              fective UID is 0, otherwise ‘$’.  Since the
770                              shell interprets ‘$’ as a special character
771                              within double quotes, it is safer in this case
772                              to escape the backslash than to try quoting it.
773                \nnn          The octal character nnn.
774                \\            Insert a single backslash character.
775                \[            Normally the shell keeps track of the number of
776                              characters in the prompt.  Use of this sequence
777                              turns off that count.
778                \]            Use of this sequence turns the count back on.
780                Note that the backslash itself may be interpreted by the
781                shell.  Hence, to set PS1 either escape the backslash itself,
782                or use double quotes.  The latter is more practical:
784                      PS1="\u "
786                This is a more complex example, which does not rely on the
787                above backslash-escaped sequences.  It embeds the current
788                working directory, in reverse video, in the prompt string:
790                      x=$(print \\001)
791                      PS1="$x$(print \\r)$x$(tput so)$x\$PWD$x$(tput se)$x> "
793     PS2        Secondary prompt string, by default ‘> ’, used when more input
794                is needed to complete a command.
796     PS3        Prompt used by the select statement when reading a menu selec‐
797                tion.  The default is ‘#? ’.
799     PS4        Used to prefix commands that are printed during execution
800                tracing (see the set -x command below).  Parameter, command,
801                and arithmetic substitutions are performed before it is
802                printed.  The default is ‘+ ’.
804     PWD        The current working directory.  May be unset or NULL if the
805                shell doesn't know where it is.
807     RANDOM     A random number generator.  Every time RANDOM is referenced,
808                it is assigned the next random number in the range 0-32767.
809                By default, arc4random(3) is used to produce values.  If the
810                variable RANDOM is assigned a value, the value is used as the
811                seed to srand_deterministic(3) and subsequent references of
812                RANDOM produce a predictable sequence.
814     REPLY      Default parameter for the read command if no names are given.
815                Also used in select loops to store the value that is read from
816                standard input.
818     SECONDS    The number of seconds since the shell started or, if the pa‐
819                rameter has been assigned an integer value, the number of sec‐
820                onds since the assignment plus the value that was assigned.
822     TERM       The user's terminal type.  If set, it will be used to deter‐
823                mine the escape sequence used to clear the screen.
825     TMOUT      If set to a positive integer in an interactive shell, it spec‐
826                ifies the maximum number of seconds the shell will wait for
827                input after printing the primary prompt (PS1).  If the time is
828                exceeded, the shell exits.
830     TMPDIR     The directory temporary shell files are created in.  If this
831                parameter is not set, or does not contain the absolute path of
832                a writable directory, temporary files are created in /tmp.
834     VISUAL     If set, this parameter controls the command-line editing mode
835                for interactive shells.  If the last component of the path
836                specified in this parameter contains the string “vi”, “emacs”,
837                or “gmacs”, the vi(1), emacs, or gmacs (Gosling emacs) editing
838                mode is enabled, respectively.  See also the EDITOR parameter,
839                above.
841   Tilde expansion
842     Tilde expansion, which is done in parallel with parameter substitution,
843     is done on words starting with an unquoted ‘~’.  The characters following
844     the tilde, up to the first ‘/’, if any, are assumed to be a login name.
845     If the login name is empty, ‘+’, or ‘-’, the value of the HOME, PWD, or
846     OLDPWD parameter is substituted, respectively.  Otherwise, the password
847     file is searched for the login name, and the tilde expression is substi‐
848     tuted with the user's home directory.  If the login name is not found in
849     the password file or if any quoting or parameter substitution occurs in
850     the login name, no substitution is performed.
852     In parameter assignments (such as those preceding a simple-command or
853     those occurring in the arguments of alias, export, readonly, and
854     typeset), tilde expansion is done after any assignment (i.e. after the
855     equals sign) or after an unquoted colon (‘:’); login names are also de‐
856     limited by colons.
858     The home directory of previously expanded login names are cached and re-
859     used.  The alias -d command may be used to list, change, and add to this
860     cache (e.g. alias -d fac=/usr/local/facilities; cd ~fac/bin).
862   Brace expansion (alternation)
863     Brace expressions take the following form:
865           prefix{str1,...,strN}suffix
867     The expressions are expanded to N words, each of which is the concatena‐
868     tion of prefix, stri, and suffix (e.g. “a{c,b{X,Y},d}e” expands to four
869     words: “ace”, “abXe”, “abYe”, and “ade”).  As noted in the example, brace
870     expressions can be nested and the resulting words are not sorted.  Brace
871     expressions must contain an unquoted comma (‘,’) for expansion to occur
872     (e.g. {} and {foo} are not expanded).  Brace expansion is carried out af‐
873     ter parameter substitution and before file name generation.
875   File name patterns
876     A file name pattern is a word containing one or more unquoted ‘?’, ‘*’,
877     ‘+’, ‘@’, or ‘!’ characters or “[..]” sequences.  Once brace expansion
878     has been performed, the shell replaces file name patterns with the sorted
879     names of all the files that match the pattern (if no files match, the
880     word is left unchanged).  The pattern elements have the following mean‐
881     ing:
883     ?       Matches any single character.
885     *       Matches any sequence of characters.
887     [..]    Matches any of the characters inside the brackets.  Ranges of
888             characters can be specified by separating two characters by a ‘-’
889             (e.g. “[a0-9]” matches the letter ‘a’ or any digit).  In order to
890             represent itself, a ‘-’ must either be quoted or the first or
891             last character in the character list.  Similarly, a ‘]’ must be
892             quoted or the first character in the list if it is to represent
893             itself instead of the end of the list.  Also, a ‘!’ appearing at
894             the start of the list has special meaning (see below), so to rep‐
895             resent itself it must be quoted or appear later in the list.
897             Within a bracket expression, the name of a character class en‐
898             closed in ‘[:’ and ‘:]’ stands for the list of all characters be‐
899             longing to that class.  Supported character classes:
901                   alnum   cntrl   lower   space
902                   alpha   digit   print   upper
903                   blank   graph   punct   xdigit
905             These match characters using the macros specified in isalnum(3),
906             isalpha(3), and so on.  A character class may not be used as an
907             endpoint of a range.
909     [!..]   Like [..], except it matches any character not inside the brack‐
910             ets.
912     *(pattern|...|pattern)
913             Matches any string of characters that matches zero or more occur‐
914             rences of the specified patterns.  Example: The pattern
915             *(foo|bar) matches the strings “”, “foo”, “bar”, “foobarfoo”,
916             etc.
918     +(pattern|...|pattern)
919             Matches any string of characters that matches one or more occur‐
920             rences of the specified patterns.  Example: The pattern
921             +(foo|bar) matches the strings “foo”, “bar”, “foobar”, etc.
923     ?(pattern|...|pattern)
924             Matches the empty string or a string that matches one of the
925             specified patterns.  Example: The pattern ?(foo|bar) only matches
926             the strings “”, “foo”, and “bar”.
928     @(pattern|...|pattern)
929             Matches a string that matches one of the specified patterns.  Ex‐
930             ample: The pattern @(foo|bar) only matches the strings “foo” and
931             “bar”.
933     !(pattern|...|pattern)
934             Matches any string that does not match one of the specified pat‐
935             terns.  Examples: The pattern !(foo|bar) matches all strings ex‐
936             cept “foo” and “bar”; the pattern !(*) matches no strings; the
937             pattern !(?)* matches all strings (think about it).
939     Unlike most shells, ksh never matches ‘.’ and ‘..’.
941     Note that none of the above pattern elements match either a period (‘.’)
942     at the start of a file name or a slash (‘/’), even if they are explicitly
943     used in a [..] sequence; also, the names ‘.’ and ‘..’ are never matched,
944     even by the pattern ‘.*’.
946     If the markdirs option is set, any directories that result from file name
947     generation are marked with a trailing ‘/’.
949   Input/output redirection
950     When a command is executed, its standard input, standard output, and
951     standard error (file descriptors 0, 1, and 2, respectively) are normally
952     inherited from the shell.  Three exceptions to this are commands in pipe‐
953     lines, for which standard input and/or standard output are those set up
954     by the pipeline, asynchronous commands created when job control is dis‐
955     abled, for which standard input is initially set to be from /dev/null,
956     and commands for which any of the following redirections have been speci‐
957     fied:
959     > file  Standard output is redirected to file.  If file does not exist,
960             it is created; if it does exist, is a regular file, and the
961             noclobber option is set, an error occurs; otherwise, the file is
962             truncated.  Note that this means the command cmd < foo > foo will
963             open foo for reading and then truncate it when it opens it for
964             writing, before cmd gets a chance to actually read foo.
966     >| file
967             Same as >, except the file is truncated, even if the noclobber
968             option is set.
970     >> file
971             Same as >, except if file exists it is appended to instead of be‐
972             ing truncated.  Also, the file is opened in append mode, so
973             writes always go to the end of the file (see open(2)).
975     < file  Standard input is redirected from file, which is opened for read‐
976             ing.
978     <> file
979             Same as <, except the file is opened for reading and writing.
981     << marker
982             After reading the command line containing this kind of redirect‐
983             ion (called a “here document”), the shell copies lines from the
984             command source into a temporary file until a line matching marker
985             is read.  When the command is executed, standard input is redi‐
986             rected from the temporary file.  If marker contains no quoted
987             characters, the contents of the temporary file are processed as
988             if enclosed in double quotes each time the command is executed,
989             so parameter, command, and arithmetic substitutions are per‐
990             formed, along with backslash (‘\’) escapes for ‘$’, ‘`’, ‘\’, and
991             ‘\newline’.  If multiple here documents are used on the same com‐
992             mand line, they are saved in order.
994     <<- marker
995             Same as <<, except leading tabs are stripped from lines in the
996             here document.
998     <& fd   Standard input is duplicated from file descriptor fd.  fd can be
999             a single digit, indicating the number of an existing file de‐
1000             scriptor; the letter ‘p’, indicating the file descriptor associ‐
1001             ated with the output of the current co-process; or the character
1002             ‘-’, indicating standard input is to be closed.
1004     >& fd   Same as <&, except the operation is done on standard output.
1006     In any of the above redirections, the file descriptor that is redirected
1007     (i.e. standard input or standard output) can be explicitly given by pre‐
1008     ceding the redirection with a single digit.  Parameter, command, and
1009     arithmetic substitutions, tilde substitutions, and (if the shell is in‐
1010     teractive) file name generation are all performed on the file, marker,
1011     and fd arguments of redirections.  Note, however, that the results of any
1012     file name generation are only used if a single file is matched; if multi‐
1013     ple files match, the word with the expanded file name generation charac‐
1014     ters is used.  Note that in restricted shells, redirections which can
1015     create files cannot be used.
1017     For simple-commands, redirections may appear anywhere in the command; for
1018     compound-commands (if statements, etc.), any redirections must appear at
1019     the end.  Redirections are processed after pipelines are created and in
1020     the order they are given, so the following will print an error with a
1021     line number prepended to it:
1023           $ cat /foo/bar 2>&1 > /dev/null | cat -n
1025   Arithmetic expressions
1026     Integer arithmetic expressions can be used with the let command, inside
1027     $((..)) expressions, inside array references (e.g. name[expr]), as nu‐
1028     meric arguments to the test command, and as the value of an assignment to
1029     an integer parameter.
1031     Expressions may contain alpha-numeric parameter identifiers, array refer‐
1032     ences, and integer constants and may be combined with the following C op‐
1033     erators (listed and grouped in increasing order of precedence):
1035     Unary operators:
1037           + - ! ~ ++ --
1039     Binary operators:
1041           ,
1042           = *= /= %= += -= <<= >>= &= ^= |=
1043           ||
1044           &&
1045           |
1046           ^
1047           &
1048           == !=
1049           < <= >= >
1050           << >>
1051           + -
1052           * / %
1054     Ternary operators:
1056           ?: (precedence is immediately higher than assignment)
1058     Grouping operators:
1060           ( )
1062     A parameter that is NULL or unset evaluates to 0.  Integer constants may
1063     be specified with arbitrary bases using the notation base#number, where
1064     base is a decimal integer specifying the base, and number is a number in
1065     the specified base.  Additionally, integers may be prefixed with ‘0X’ or
1066     ‘0x’ (specifying base 16) or ‘0’ (base 8) in all forms of arithmetic ex‐
1067     pressions, except as numeric arguments to the test command.
1069     The operators are evaluated as follows:
1071           unary +
1072                   Result is the argument (included for completeness).
1074           unary -
1075                   Negation.
1077           !       Logical NOT; the result is 1 if argument is zero, 0 if not.
1079           ~       Arithmetic (bit-wise) NOT.
1081           ++      Increment; must be applied to a parameter (not a literal or
1082                   other expression).  The parameter is incremented by 1.
1083                   When used as a prefix operator, the result is the incre‐
1084                   mented value of the parameter; when used as a postfix oper‐
1085                   ator, the result is the original value of the parameter.
1087           --      Similar to ++, except the parameter is decremented by 1.
1089           ,       Separates two arithmetic expressions; the left-hand side is
1090                   evaluated first, then the right.  The result is the value
1091                   of the expression on the right-hand side.
1093           =       Assignment; the variable on the left is set to the value on
1094                   the right.
1096           *= /= += -= <<= >>= &= ^= |=
1097                   Assignment operators.  ⟨var⟩⟨op⟩=⟨expr⟩ is the same as
1098var⟩=⟨var⟩⟨op⟩⟨expr⟩, with any operator precedence in
1099expr⟩ preserved.  For example, “var1 *= 5 + 3” is the same
1100                   as specifying “var1 = var1 * (5 + 3)”.
1102           ||      Logical OR; the result is 1 if either argument is non-zero,
1103                   0 if not.  The right argument is evaluated only if the left
1104                   argument is zero.
1106           &&      Logical AND; the result is 1 if both arguments are non-
1107                   zero, 0 if not.  The right argument is evaluated only if
1108                   the left argument is non-zero.
1110           |       Arithmetic (bit-wise) OR.
1112           ^       Arithmetic (bit-wise) XOR (exclusive-OR).
1114           &       Arithmetic (bit-wise) AND.
1116           ==      Equal; the result is 1 if both arguments are equal, 0 if
1117                   not.
1119           !=      Not equal; the result is 0 if both arguments are equal, 1
1120                   if not.
1122           <       Less than; the result is 1 if the left argument is less
1123                   than the right, 0 if not.
1125           <= >= >
1126                   Less than or equal, greater than or equal, greater than.
1127                   See <.
1129           << >>   Shift left (right); the result is the left argument with
1130                   its bits shifted left (right) by the amount given in the
1131                   right argument.
1133           + - * /
1134                   Addition, subtraction, multiplication, and division.
1136           %       Remainder; the result is the remainder of the division of
1137                   the left argument by the right.  The sign of the result is
1138                   unspecified if either argument is negative.
1141                   If ⟨arg1⟩ is non-zero, the result is ⟨arg2⟩; otherwise the
1142                   result is ⟨arg3⟩.
1144   Co-processes
1145     A co-process, which is a pipeline created with the ‘|&’ operator, is an
1146     asynchronous process that the shell can both write to (using print -p)
1147     and read from (using read -p).  The input and output of the co-process
1148     can also be manipulated using >&p and <&p redirections, respectively.
1149     Once a co-process has been started, another can't be started until the
1150     co-process exits, or until the co-process's input has been redirected us‐
1151     ing an exec n>&p redirection.  If a co-process's input is redirected in
1152     this way, the next co-process to be started will share the output with
1153     the first co-process, unless the output of the initial co-process has
1154     been redirected using an exec n<&p redirection.
1156     Some notes concerning co-processes:
1158     The only way to close the co-process's input (so the co-process reads
1159         an end-of-file) is to redirect the input to a numbered file descrip‐
1160         tor and then close that file descriptor e.g. exec 3>&p; exec 3>&-.
1162     In order for co-processes to share a common output, the shell must
1163         keep the write portion of the output pipe open.  This means that end-
1164         of-file will not be detected until all co-processes sharing the co-
1165         process's output have exited (when they all exit, the shell closes
1166         its copy of the pipe).  This can be avoided by redirecting the output
1167         to a numbered file descriptor (as this also causes the shell to close
1168         its copy).  Note that this behaviour is slightly different from the
1169         original Korn shell which closes its copy of the write portion of the
1170         co-process output when the most recently started co-process (instead
1171         of when all sharing co-processes) exits.
1173     •   print -p will ignore SIGPIPE signals during writes if the signal is
1174         not being trapped or ignored; the same is true if the co-process in‐
1175         put has been duplicated to another file descriptor and print -un is
1176         used.
1178   Functions
1179     Functions are defined using either Korn shell function function-name syn‐
1180     tax or the Bourne/POSIX shell function-name() syntax (see below for the
1181     difference between the two forms).  Functions are like .-scripts (i.e.
1182     scripts sourced using the ‘.’ built-in) in that they are executed in the
1183     current environment.  However, unlike .-scripts, shell arguments (i.e.
1184     positional parameters $1, $2, etc.) are never visible inside them.  When
1185     the shell is determining the location of a command, functions are
1186     searched after special built-in commands, before regular and non-regular
1187     built-ins, and before the PATH is searched.
1189     An existing function may be deleted using unset -f function-name.  A list
1190     of functions can be obtained using typeset +f and the function defini‐
1191     tions can be listed using typeset -f.  The autoload command (which is an
1192     alias for typeset -fu) may be used to create undefined functions: when an
1193     undefined function is executed, the shell searches the path specified in
1194     the FPATH parameter for a file with the same name as the function, which,
1195     if found, is read and executed.  If after executing the file the named
1196     function is found to be defined, the function is executed; otherwise, the
1197     normal command search is continued (i.e. the shell searches the regular
1198     built-in command table and PATH).  Note that if a command is not found
1199     using PATH, an attempt is made to autoload a function using FPATH (this
1200     is an undocumented feature of the original Korn shell).
1202     Functions can have two attributes, “trace” and “export”, which can be set
1203     with typeset -ft and typeset -fx, respectively.  When a traced function
1204     is executed, the shell's xtrace option is turned on for the function's
1205     duration; otherwise, the xtrace option is turned off.  The “export” at‐
1206     tribute of functions is currently not used.  In the original Korn shell,
1207     exported functions are visible to shell scripts that are executed.
1209     Since functions are executed in the current shell environment, parameter
1210     assignments made inside functions are visible after the function com‐
1211     pletes.  If this is not the desired effect, the typeset command can be
1212     used inside a function to create a local parameter.  Note that special
1213     parameters (e.g. $$, $!) can't be scoped in this way.
1215     The exit status of a function is that of the last command executed in the
1216     function.  A function can be made to finish immediately using the return
1217     command; this may also be used to explicitly specify the exit status.
1219     Functions defined with the function reserved word are treated differently
1220     in the following ways from functions defined with the () notation:
1222     The $0 parameter is set to the name of the function (Bourne-style
1223         functions leave $0 untouched).
1225     Parameter assignments preceding function calls are not kept in the
1226         shell environment (executing Bourne-style functions will keep assign‐
1227         ments).
1229     OPTIND is saved/reset and restored on entry and exit from the func‐
1230         tion so getopts can be used properly both inside and outside the
1231         function (Bourne-style functions leave OPTIND untouched, so using
1232         getopts inside a function interferes with using getopts outside the
1233         function).
1235   POSIX mode
1236     The shell is intended to be POSIX compliant; however, in some cases,
1237     POSIX behaviour is contrary either to the original Korn shell behaviour
1238     or to user convenience.  How the shell behaves in these cases is deter‐
1239     mined by the state of the posix option (set -o posix).  If it is on, the
1240     POSIX behaviour is followed; otherwise, it is not.  The posix option is
1241     set automatically when the shell starts up if the environment contains
1242     the POSIXLY_CORRECT parameter.  The shell can also be compiled so that it
1243     is in POSIX mode by default; however, this is usually not desirable.
1245     The following is a list of things that are affected by the state of the
1246     posix option:
1248     •   kill -l output.  In POSIX mode, only signal names are listed (in a
1249         single line); in non-POSIX mode, signal numbers, names, and descrip‐
1250         tions are printed (in columns).
1252     •   echo options.  In POSIX mode, -e and -E are not treated as options,
1253         but printed like other arguments; in non-POSIX mode, these options
1254         control the interpretation of backslash sequences.
1256     •   fg exit status.  In POSIX mode, the exit status is 0 if no errors oc‐
1257         cur; in non-POSIX mode, the exit status is that of the last fore‐
1258         grounded job.
1260     •   eval exit status.  If eval gets to see an empty command (i.e. eval
1261         `false`), its exit status in POSIX mode will be 0.  In non-POSIX
1262         mode, it will be the exit status of the last command substitution
1263         that was done in the processing of the arguments to eval (or 0 if
1264         there were no command substitutions).
1266     •   getopts.  In POSIX mode, options must start with a ‘-’; in non-POSIX
1267         mode, options can start with either ‘-’ or ‘+’.
1269     Brace expansion (also known as alternation).  In POSIX mode, brace
1270         expansion is disabled; in non-POSIX mode, brace expansion is enabled.
1271         Note that set -o posix (or setting the POSIXLY_CORRECT parameter) au‐
1272         tomatically turns the braceexpand option off; however, it can be ex‐
1273         plicitly turned on later.
1275     •   set -.  In POSIX mode, this does not clear the verbose or xtrace op‐
1276         tions; in non-POSIX mode, it does.
1278     •   set exit status.  In POSIX mode, the exit status of set is 0 if there
1279         are no errors; in non-POSIX mode, the exit status is that of any com‐
1280         mand substitutions performed in generating the set command.  For ex‐
1281         ample, set -- `false`; echo $? prints 0 in POSIX mode, 1 in non-POSIX
1282         mode.  This construct is used in most shell scripts that use the old
1283         getopt(1) command.
1285     Argument expansion of the alias, export, readonly, and typeset com‐
1286         mands.  In POSIX mode, normal argument expansion is done; in non-
1287         POSIX mode, field splitting, file globbing, brace expansion, and
1288         (normal) tilde expansion are turned off, while assignment tilde ex‐
1289         pansion is turned on.
1291     Signal specification.  In POSIX mode, signals can be specified as
1292         digits, only if signal numbers match POSIX values (i.e. HUP=1, INT=2,
1293         QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15); in non-POSIX mode,
1294         signals can always be digits.
1296     Alias expansion.  In POSIX mode, alias expansion is only carried out
1297         when reading command words; in non-POSIX mode, alias expansion is
1298         carried out on any word following an alias that ended in a space.
1299         For example, the following for loop uses parameter ‘i’ in POSIX mode
1300         and ‘j’ in non-POSIX mode:
1302               alias a='for ' i='j'
1303               a i in 1 2; do echo i=$i j=$j; done
1305     •   test.  In POSIX mode, the expression ‘-t’ (preceded by some number of
1306         ‘!’ arguments) is always true as it is a non-zero length string; in
1307         non-POSIX mode, it tests if file descriptor 1 is a tty(4) (i.e. the
1308         fd argument to the -t test may be left out and defaults to 1).
1310   Strict Bourne shell mode
1311     When the sh option is enabled (see the set command), oksh will behave
1312     like sh(1) in the following ways:
1314     The parameter $_ is not set to:
1316         -   the expanded alias' full program path after entering commands
1317             that are tracked aliases
1318         -   the last argument on the command line after entering external
1319             commands
1320         -   the file that changed when MAILPATH is set to monitor a mailbox
1322     File descriptors are left untouched when executing exec with no argu‐
1323         ments.
1325     Backslash-escaped special characters are not substituted in PS1.
1327     Sequences of ‘((...))’ are not interpreted as arithmetic expressions.
1329   Command execution
1330     After evaluation of command-line arguments, redirections, and parameter
1331     assignments, the type of command is determined: a special built-in, a
1332     function, a regular built-in, or the name of a file to execute found us‐
1333     ing the PATH parameter.  The checks are made in the above order.  Special
1334     built-in commands differ from other commands in that the PATH parameter
1335     is not used to find them, an error during their execution can cause a
1336     non-interactive shell to exit, and parameter assignments that are speci‐
1337     fied before the command are kept after the command completes.  Just to
1338     confuse things, if the posix option is turned off (see the set command
1339     below), some special commands are very special in that no field split‐
1340     ting, file globbing, brace expansion, nor tilde expansion is performed on
1341     arguments that look like assignments.  Regular built-in commands are dif‐
1342     ferent only in that the PATH parameter is not used to find them.
1344     The original ksh and POSIX differ somewhat in which commands are consid‐
1345     ered special or regular:
1347     POSIX special commands
1349     ., :, break, continue, eval, exec, exit, export, readonly, return, set,
1350     shift, times, trap, unset
1352     Additional oksh special commands
1354     builtin, typeset
1356     Very special commands (when POSIX mode is off)
1358     alias, readonly, set, typeset
1360     POSIX regular commands
1362     alias, bg, cd, command, false, fc, fg, getopts, jobs, kill, pwd, read,
1363     true, umask, unalias, wait
1365     Additional oksh regular commands
1367     [, echo, let, print, suspend, test, ulimit, whence
1369     Once the type of command has been determined, any command-line parameter
1370     assignments are performed and exported for the duration of the command.
1372     The following describes the special and regular built-in commands:
1374     . file [arg ...]
1375             Execute the commands in file in the current environment.  The
1376             file is searched for in the directories of PATH.  If arguments
1377             are given, the positional parameters may be used to access them
1378             while file is being executed.  If no arguments are given, the po‐
1379             sitional parameters are those of the environment the command is
1380             used in.
1382     : [...]
1383             The null command.  Exit status is set to zero.
1385     alias [-d | -t [-r] | +-x] [-p] [+] [name [=value] ...]
1386             Without arguments, alias lists all aliases.  For any name without
1387             a value, the existing alias is listed.  Any name with a value de‐
1388             fines an alias (see Aliases above).
1390             When listing aliases, one of two formats is used.  Normally,
1391             aliases are listed as name=value, where value is quoted.  If op‐
1392             tions were preceded with ‘+’, or a lone ‘+’ is given on the com‐
1393             mand line, only name is printed.
1395             The -d option causes directory aliases, which are used in tilde
1396             expansion, to be listed or set (see Tilde expansion above).
1398             If the -p option is used, each alias is prefixed with the string
1399             “alias ”.
1401             The -t option indicates that tracked aliases are to be listed/set
1402             (values specified on the command line are ignored for tracked
1403             aliases).  The -r option indicates that all tracked aliases are
1404             to be reset.
1406             The -x option sets (+x clears) the export attribute of an alias
1407             or, if no names are given, lists the aliases with the export at‐
1408             tribute (exporting an alias has no effect).
1410     bg [job ...]
1411             Resume the specified stopped job(s) in the background.  If no
1412             jobs are specified, %+ is assumed.  See Job control below for
1413             more information.
1415     bind [-l]
1416             The current bindings are listed.  If the -l flag is given, bind
1417             instead lists the names of the functions to which keys may be
1418             bound.  See Emacs editing mode for more information.
1420     bind [-m] string=[substitute] ...
1421     bind string=[editing-command] ...
1422             In Emacs editing mode, the specified editing command is bound to
1423             the given string.  Future input of the string will cause the
1424             editing command to be immediately invoked.  Bindings have no ef‐
1425             fect in Vi editing mode.
1427             If the -m flag is given, the specified input string will after‐
1428             wards be immediately replaced by the given substitute string,
1429             which may contain editing commands.  Control characters may be
1430             written using caret notation.  For example, ^X represents Con‐
1431             trol-X.
1433             If a certain character occurs as the first character of any bound
1434             multi-character string sequence, that character becomes a command
1435             prefix character.  Any character sequence that starts with a com‐
1436             mand prefix character but that is not bound to a command or sub‐
1437             stitute is implicitly considered as bound to the ‘error’ command.
1438             By default, two command prefix characters exist: Escape (^[) and
1439             Control-X (^X).
1441             The following default bindings show how the arrow keys on an ANSI
1442             terminal or xterm are bound (of course some escape sequences
1443             won't work out quite this nicely):
1445                   bind '^[[A'=up-history
1446                   bind '^[[B'=down-history
1447                   bind '^[[C'=forward-char
1448                   bind '^[[D'=backward-char
1450     break [level]
1451             Exit the levelth inner-most for, select, until, or while loop.
1452             level defaults to 1.
1454     builtin command [arg ...]
1455             Execute the built-in command command.
1457     cd [-LP] [dir]
1458             Set the working directory to dir.  If the parameter CDPATH is
1459             set, it lists the search path for the directory containing dir.
1460             A NULL path means the current directory.  If dir is found in any
1461             component of the CDPATH search path other than the NULL path, the
1462             name of the new working directory will be written to standard
1463             output.  If dir is missing, the home directory HOME is used.  If
1464             dir is ‘-’, the previous working directory is used (see the
1465             OLDPWD parameter).
1467             If the -L option (logical path) is used or if the physical option
1468             isn't set (see the set command below), references to ‘..’ in dir
1469             are relative to the path used to get to the directory.  If the -P
1470             option (physical path) is used or if the physical option is set,
1471             ‘..’ is relative to the filesystem directory tree.  The PWD and
1472             OLDPWD parameters are updated to reflect the current and old
1473             working directory, respectively.
1475     cd [-LP] old new
1476             The string new is substituted for old in the current directory,
1477             and the shell attempts to change to the new directory.
1479     command [-pVv] cmd [arg ...]
1480             If neither the -v nor -V option is given, cmd is executed exactly
1481             as if command had not been specified, with two exceptions:
1482             firstly, cmd cannot be an alias or a shell function; and sec‐
1483             ondly, special built-in commands lose their specialness (i.e. re‐
1484             direction and utility errors do not cause the shell to exit, and
1485             command assignments are not permanent).
1487             If the -p option is given, a default search path is used instead
1488             of the current value of PATH (the actual value of the default
1489             path is system dependent: on POSIX-ish systems, it is the value
1490             returned by getconf PATH).  Nevertheless, reserved words,
1491             aliases, shell functions, and builtin commands are still found
1492             before external commands.
1494             If the -v option is given, instead of executing cmd, information
1495             about what would be executed is given (and the same is done for
1496             arg ...).  For special and regular built-in commands and func‐
1497             tions, their names are simply printed; for aliases, a command
1498             that defines them is printed; and for commands found by searching
1499             the PATH parameter, the full path of the command is printed.  If
1500             no command is found (i.e. the path search fails), nothing is
1501             printed and command exits with a non-zero status.  The -V option
1502             is like the -v option, except it is more verbose.
1504     continue [level]
1505             Jumps to the beginning of the levelth inner-most for, select,
1506             until, or while loop.  level defaults to 1.
1508     echo [-Een] [arg ...]
1509             Prints its arguments (separated by spaces) followed by a newline,
1510             to the standard output.  The newline is suppressed if any of the
1511             arguments contain the backslash sequence ‘\c’.  See the print
1512             command below for a list of other backslash sequences that are
1513             recognized.
1515             The options are provided for compatibility with BSD shell
1516             scripts.  The -n option suppresses the trailing newline, -e en‐
1517             ables backslash interpretation (a no-op, since this is normally
1518             done), and -E suppresses backslash interpretation.  If the posix
1519             option is set, only the first argument is treated as an option,
1520             and only if it is exactly “-n”.
1522     eval command ...
1523             The arguments are concatenated (with spaces between them) to form
1524             a single string which the shell then parses and executes in the
1525             current environment.
1527     exec [command [arg ...]]
1528             The command is executed without forking, replacing the shell
1529             process.
1531             If no command is given except for I/O redirection, the I/O redi‐
1532             rection is permanent and the shell is not replaced.  Any file de‐
1533             scriptors greater than 2 which are opened or dup(2)'d in this way
1534             are not made available to other executed commands (i.e. commands
1535             that are not built-in to the shell).  Note that the Bourne shell
1536             differs here; it does pass these file descriptors on.
1538     exit [status]
1539             The shell exits with the specified exit status.  If status is not
1540             specified, the exit status is the current value of the $? parame‐
1541             ter.
1543     export [-p] [parameter[=value]]
1544             Sets the export attribute of the named parameters.  Exported pa‐
1545             rameters are passed in the environment to executed commands.  If
1546             values are specified, the named parameters are also assigned.
1548             If no parameters are specified, the names of all parameters with
1549             the export attribute are printed one per line, unless the -p op‐
1550             tion is used, in which case export commands defining all exported
1551             parameters, including their values, are printed.
1553     false   A command that exits with a non-zero status.
1555     fc [-e editor | -l [-n]] [-r] [first [last]]
1556             Fix command.  first and last select commands from the history.
1557             Commands can be selected by history number or a string specifying
1558             the most recent command starting with that string.  The -l option
1559             lists the command on standard output, and -n inhibits the default
1560             command numbers.  The -r option reverses the order of the list.
1561             Without -l, the selected commands are edited by the editor speci‐
1562             fied with the -e option, or if no -e is specified, the editor
1563             specified by the FCEDIT parameter (if this parameter is not set,
1564             /bin/ed is used), and then executed by the shell.
1566     fc -s [-g] [old=new] [prefix]
1567             Re-execute the most recent command beginning with prefix, or the
1568             previous command if no prefix is specified, performing the op‐
1569             tional substitution of old with new.  If -g is specified, all oc‐
1570             currences of old are replaced with new.  The editor is not in‐
1571             voked when the -s flag is used.  The obsolescent equivalent “-e
1572             -” is also accepted.  This command is usually accessed with the
1573             predefined alias r='fc -s'.
1575     fg [job ...]
1576             Resume the specified job(s) in the foreground.  If no jobs are
1577             specified, %+ is assumed.  See Job control below for more infor‐
1578             mation.
1580     getopts optstring name [arg ...]
1581             Used by shell procedures to parse the specified arguments (or po‐
1582             sitional parameters, if no arguments are given) and to check for
1583             legal options.  optstring contains the option letters that
1584             getopts is to recognize.  If a letter is followed by a colon, the
1585             option is expected to have an argument.  Options that do not take
1586             arguments may be grouped in a single argument.  If an option
1587             takes an argument and the option character is not the last char‐
1588             acter of the argument it is found in, the remainder of the argu‐
1589             ment is taken to be the option's argument; otherwise, the next
1590             argument is the option's argument.
1592             Each time getopts is invoked, it places the next option in the
1593             shell parameter name and the index of the argument to be pro‐
1594             cessed by the next call to getopts in the shell parameter OPTIND.
1595             If the option was introduced with a ‘+’, the option placed in
1596             name is prefixed with a ‘+’.  When an option requires an argu‐
1597             ment, getopts places it in the shell parameter OPTARG.
1599             When an illegal option or a missing option argument is encoun‐
1600             tered, a question mark or a colon is placed in name (indicating
1601             an illegal option or missing argument, respectively) and OPTARG
1602             is set to the option character that caused the problem.  Further‐
1603             more, if optstring does not begin with a colon, a question mark
1604             is placed in name, OPTARG is unset, and an error message is
1605             printed to standard error.
1607             When the end of the options is encountered, getopts exits with a
1608             non-zero exit status.  Options end at the first (non-option argu‐
1609             ment) argument that does not start with a ‘-’, or when a ‘--’ ar‐
1610             gument is encountered.
1612             Option parsing can be reset by setting OPTIND to 1 (this is done
1613             automatically whenever the shell or a shell procedure is in‐
1614             voked).
1616             Warning: Changing the value of the shell parameter OPTIND to a
1617             value other than 1, or parsing different sets of arguments with‐
1618             out resetting OPTIND, may lead to unexpected results.
1620     hash [-r] [name ...]
1621             Without arguments, any hashed executable command pathnames are
1622             listed.  The -r option causes all hashed commands to be removed
1623             from the hash table.  Each name is searched as if it were a com‐
1624             mand name and added to the hash table if it is an executable com‐
1625             mand.
1627     jobs [-lnp] [job ...]
1628             Display information about the specified job(s); if no jobs are
1629             specified, all jobs are displayed.  The -n option causes informa‐
1630             tion to be displayed only for jobs that have changed state since
1631             the last notification.  If the -l option is used, the process ID
1632             of each process in a job is also listed.  The -p option causes
1633             only the process group of each job to be printed.  See Job
1634             control below for the format of job and the displayed job.
1636     kill [-s signame | -signum | -signame] { job | pid | pgrp } ...
1637             Send the specified signal to the specified jobs, process IDs, or
1638             process groups.  If no signal is specified, the TERM signal is
1639             sent.  If a job is specified, the signal is sent to the job's
1640             process group.  See Job control below for the format of job.
1642     kill -l [exit-status ...]
1643             Print the signal name corresponding to exit-status.  If no argu‐
1644             ments are specified, a list of all the signals, their numbers,
1645             and a short description of them are printed.
1647     let [expression ...]
1648             Each expression is evaluated (see Arithmetic expressions above).
1649             If all expressions are successfully evaluated, the exit status is
1650             0 (1) if the last expression evaluated to non-zero (zero).  If an
1651             error occurs during the parsing or evaluation of an expression,
1652             the exit status is greater than 1.  Since expressions may need to
1653             be quoted, (( expr )) is syntactic sugar for let "expr".
1655     print [-nprsu[n] | -R [-en]] [argument ...]
1656             print prints its arguments on the standard output, separated by
1657             spaces and terminated with a newline.  The -n option suppresses
1658             the newline.  By default, certain C escapes are translated.
1659             These include ‘\b’, ‘\f’, ‘\n’, ‘\r’, ‘\t’, ‘\v’, and ‘\0###’
1660             (‘#’ is an octal digit, of which there may be 0 to 3).  ‘\c’ is
1661             equivalent to using the -n option.  ‘\’ expansion may be inhib‐
1662             ited with the -r option.  The -s option prints to the history
1663             file instead of standard output; the -u option prints to file de‐
1664             scriptor n (n defaults to 1 if omitted); and the -p option prints
1665             to the co-process (see Co-processes above).
1667             The -R option is used to emulate, to some degree, the BSD echo(1)
1668             command, which does not process ‘\’ sequences unless the -e op‐
1669             tion is given.  As above, the -n option suppresses the trailing
1670             newline.
1672     pwd [-LP]
1673             Print the present working directory.  If the -L option is used or
1674             if the physical option isn't set (see the set command below), the
1675             logical path is printed (i.e. the path used to cd to the current
1676             directory).  If the -P option (physical path) is used or if the
1677             physical option is set, the path determined from the filesystem
1678             (by following ‘..’ directories to the root directory) is printed.
1680     read [-prsu[n]] [parameter ...]
1681             Reads a line of input from the standard input, separates the line
1682             into fields using the IFS parameter (see Substitution above), and
1683             assigns each field to the specified parameters.  If there are
1684             more parameters than fields, the extra parameters are set to
1685             NULL, or alternatively, if there are more fields than parameters,
1686             the last parameter is assigned the remaining fields (inclusive of
1687             any separating spaces).  If no parameters are specified, the
1688             REPLY parameter is used.  If the input line ends in a backslash
1689             and the -r option was not used, the backslash and the newline are
1690             stripped and more input is read.  If no input is read, read exits
1691             with a non-zero status.
1693             The first parameter may have a question mark and a string ap‐
1694             pended to it, in which case the string is used as a prompt
1695             (printed to standard error before any input is read) if the input
1696             is a tty(4) (e.g. read nfoo?'number of foos: ').
1698             The -un and -p options cause input to be read from file descrip‐
1699             tor n (n defaults to 0 if omitted) or the current co-process (see
1700             Co-processes above for comments on this), respectively.  If the
1701             -s option is used, input is saved to the history file.
1703     readonly [-p] [parameter [=value] ...]
1704             Sets the read-only attribute of the named parameters.  If values
1705             are given, parameters are set to them before setting the attri‐
1706             bute.  Once a parameter is made read-only, it cannot be unset and
1707             its value cannot be changed.
1709             If no parameters are specified, the names of all parameters with
1710             the read-only attribute are printed one per line, unless the -p
1711             option is used, in which case readonly commands defining all
1712             read-only parameters, including their values, are printed.
1714     return [status]
1715             Returns from a function or . script, with exit status status.  If
1716             no status is given, the exit status of the last executed command
1717             is used.  If used outside of a function or . script, it has the
1718             same effect as exit.  Note that ksh treats both profile and ENV
1719             files as . scripts, while the original Korn shell only treats
1720             profiles as . scripts.
1722     set [+-abCefhkmnpsuvXx] [+-o option] [+-A name] [--] [arg ...]
1723             The set command can be used to set (-) or clear (+) shell op‐
1724             tions, set the positional parameters, or set an array parameter.
1725             Options can be changed using the +-o option syntax, where option
1726             is the long name of an option, or using the +-letter syntax,
1727             where letter is the option's single letter name (not all options
1728             have a single letter name).  The following table lists both op‐
1729             tion letters (if they exist) and long names along with a descrip‐
1730             tion of what the option does:
1732             -A name          Sets the elements of the array parameter name to
1733                              arg ... If -A is used, the array is reset (i.e.
1734                              emptied) first; if +A is used, the first N ele‐
1735                              ments are set (where N is the number of argu‐
1736                              ments); the rest are left untouched.
1738             -a | allexport   All new parameters are created with the export
1739                              attribute.
1741             -b | notify      Print job notification messages asynchronously,
1742                              instead of just before the prompt.  Only used if
1743                              job control is enabled (-m).
1745             -C | noclobber   Prevent > redirection from overwriting existing
1746                              files.  Instead, >| must be used to force an
1747                              overwrite.
1749             -e | errexit     Exit (after executing the ERR trap) as soon as
1750                              an error occurs or a command fails (i.e. exits
1751                              with a non-zero status).  This does not apply to
1752                              commands whose exit status is explicitly tested
1753                              by a shell construct such as if, until, while,
1754                              or ! statements.  For && or ||, only the status
1755                              of the last command is tested.
1757             -f | noglob      Do not expand file name patterns.
1759             -h | trackall    Create tracked aliases for all executed commands
1760                              (see Aliases above).  Enabled by default for
1761                              non-interactive shells.
1763             -k | keyword     Parameter assignments are recognized anywhere in
1764                              a command.
1766             -m | monitor     Enable job control (default for interactive
1767                              shells).
1769             -n | noexec      Do not execute any commands.  Useful for check‐
1770                              ing the syntax of scripts (ignored if interac‐
1771                              tive).
1773             -p | privileged  The shell is a privileged shell.  It is set au‐
1774                              tomatically if, when the shell starts, the real
1775                              UID or GID does not match the effective UID
1776                              (EUID) or GID (EGID), respectively.  See above
1777                              for a description of what this means.
1779             -s | stdin       If used when the shell is invoked, commands are
1780                              read from standard input.  Set automatically if
1781                              the shell is invoked with no arguments.
1783                              When -s is used with the set command it causes
1784                              the specified arguments to be sorted before as‐
1785                              signing them to the positional parameters (or to
1786                              array name, if -A is used).
1788             -u | nounset     Referencing of an unset parameter is treated as
1789                              an error, unless one of the ‘-’, ‘+’, or ‘=’
1790                              modifiers is used.
1792             -v | verbose     Write shell input to standard error as it is
1793                              read.
1795             -X | markdirs    Mark directories with a trailing ‘/’ during file
1796                              name generation.
1798             -x | xtrace      Print commands and parameter assignments when
1799                              they are executed, preceded by the value of PS4.
1801             bgnice           Background jobs are run with lower priority.
1803             braceexpand      Enable brace expansion (a.k.a. alternation).
1805             csh-history      Enables a subset of csh(1)-style history editing
1806                              using the ‘!’ character.
1808             emacs            Enable BRL emacs-like command-line editing (in‐
1809                              teractive shells only); see Emacs editing mode.
1811             gmacs            Enable gmacs-like command-line editing (interac‐
1812                              tive shells only).  Currently identical to emacs
1813                              editing except that transpose (^T) acts slightly
1814                              differently.
1816             ignoreeof        The shell will not (easily) exit when end-of-
1817                              file is read; exit must be used.  To avoid infi‐
1818                              nite loops, the shell will exit if EOF is read
1819                              13 times in a row.
1821             interactive      The shell is an interactive shell.  This option
1822                              can only be used when the shell is invoked.  See
1823                              above for a description of what this means.
1825             login            The shell is a login shell.  This option can
1826                              only be used when the shell is invoked.  See
1827                              above for a description of what this means.
1829             nohup            Do not kill running jobs with a SIGHUP signal
1830                              when a login shell exits.  Currently set by de‐
1831                              fault; this is different from the original Korn
1832                              shell (which doesn't have this option, but does
1833                              send the SIGHUP signal).
1835             nolog            No effect.  In the original Korn shell, this
1836                              prevents function definitions from being stored
1837                              in the history file.
1839             physical         Causes the cd and pwd commands to use “physical”
1840                              (i.e. the filesystem's) ‘..’ directories instead
1841                              of “logical” directories (i.e. the shell handles
1842                              ‘..’, which allows the user to be oblivious of
1843                              symbolic links to directories).  Clear by de‐
1844                              fault.  Note that setting this option does not
1845                              affect the current value of the PWD parameter;
1846                              only the cd command changes PWD.  See the cd and
1847                              pwd commands above for more details.
1849             posix            Enable POSIX mode.  See POSIX mode above.
1851             restricted       The shell is a restricted shell.  This option
1852                              can only be used when the shell is invoked.  See
1853                              above for a description of what this means.
1855             sh               Enable strict Bourne shell mode (see Strict
1856                              Bourne shell mode above).
1858             vi               Enable vi(1)-like command-line editing (interac‐
1859                              tive shells only).
1861             vi-esccomplete   In vi command-line editing, do command and file
1862                              name completion when escape (^[) is entered in
1863                              command mode.
1865             vi-show8         Prefix characters with the eighth bit set with
1866                              ‘M-’.  If this option is not set, characters in
1867                              the range 128-160 are printed as is, which may
1868                              cause problems.
1870             vi-tabcomplete   In vi command-line editing, do command and file
1871                              name completion when tab (^I) is entered in in‐
1872                              sert mode.  This is the default.
1874             viraw            No effect.  In the original Korn shell, unless
1875                              viraw was set, the vi command-line mode would
1876                              let the tty(4) driver do the work until ESC (^[)
1877                              was entered.  ksh is always in viraw mode.
1879             These options can also be used upon invocation of the shell.  The
1880             current set of options (with single letter names) can be found in
1881             the parameter ‘$-’.  set -o with no option name will list all the
1882             options and whether each is on or off; set +o will print the cur‐
1883             rent shell options in a form that can be reinput to the shell to
1884             achieve the same option settings.
1886             Remaining arguments, if any, are positional parameters and are
1887             assigned, in order, to the positional parameters (i.e. $1, $2,
1888             etc.).  If options end with ‘--’ and there are no remaining argu‐
1889             ments, all positional parameters are cleared.  If no options or
1890             arguments are given, the values of all names are printed.  For
1891             unknown historical reasons, a lone ‘-’ option is treated spe‐
1892             cially - it clears both the -x and -v options.
1894     shift [number]
1895             The positional parameters number+1, number+2, etc. are renamed to
1896             ‘1’, ‘2’, etc.  number defaults to 1.
1898     suspend
1899             Stops the shell as if it had received the suspend character from
1900             the terminal.  It is not possible to suspend a login shell unless
1901             the parent process is a member of the same terminal session but
1902             is a member of a different process group.  As a general rule, if
1903             the shell was started by another shell or via su(1), it can be
1904             suspended.
1906     test expression
1907     [ expression ]
1908             test evaluates the expression and returns zero status if true, 1
1909             if false, or greater than 1 if there was an error.  It is nor‐
1910             mally used as the condition command of if and while statements.
1911             Symbolic links are followed for all file expressions except -h
1912             and -L.
1914             The following basic expressions are available:
1916             -a file            file exists.
1918             -b file            file is a block special device.
1920             -c file            file is a character special device.
1922             -d file            file is a directory.
1924             -e file            file exists.
1926             -f file            file is a regular file.
1928             -G file            file's group is the shell's effective group
1929                                ID.
1931             -g file            file's mode has the setgid bit set.
1933             -h file            file is a symbolic link.
1935             -k file            file's mode has the sticky(8) bit set.
1937             -L file            file is a symbolic link.
1939             -O file            file's owner is the shell's effective user ID.
1941             -o option          Shell option is set (see the set command above
1942                                for a list of options).  As a non-standard ex‐
1943                                tension, if the option starts with a ‘!’, the
1944                                test is negated; the test always fails if
1945                                option doesn't exist (so [ -o foo -o -o !foo ]
1946                                returns true if and only if option foo ex‐
1947                                ists).
1949             -p file            file is a named pipe.
1951             -r file            file exists and is readable.
1953             -S file            file is a unix(4)-domain socket.
1955             -s file            file is not empty.
1957             -t [fd]            File descriptor fd is a tty(4) device.  If the
1958                                posix option is not set, fd may be left out,
1959                                in which case it is taken to be 1 (the behav‐
1960                                iour differs due to the special POSIX rules
1961                                described above).
1963             -u file            file's mode has the setuid bit set.
1965             -w file            file exists and is writable.
1967             -x file            file exists and is executable.
1969             file1 -nt file2    file1 is newer than file2 or file1 exists and
1970                                file2 does not.
1972             file1 -ot file2    file1 is older than file2 or file2 exists and
1973                                file1 does not.
1975             file1 -ef file2    file1 is the same file as file2.
1977             string             string has non-zero length.
1979             -n string          string is not empty.
1981             -z string          string is empty.
1983             string = string    Strings are equal.
1985             string == string   Strings are equal.
1987             string != string   Strings are not equal.
1989             number -eq number  Numbers compare equal.
1991             number -ne number  Numbers compare not equal.
1993             number -ge number  Numbers compare greater than or equal.
1995             number -gt number  Numbers compare greater than.
1997             number -le number  Numbers compare less than or equal.
1999             number -lt number  Numbers compare less than.
2001             The above basic expressions, in which unary operators have prece‐
2002             dence over binary operators, may be combined with the following
2003             operators (listed in increasing order of precedence):
2005                   expr -o expr            Logical OR.
2006                   expr -a expr            Logical AND.
2007                   ! expr                  Logical NOT.
2008                   ( expr )                Grouping.
2010             On operating systems not supporting /dev/fd/n devices (where n is
2011             a file descriptor number), the test command will attempt to fake
2012             it for all tests that operate on files (except the -e test).  For
2013             example, [ -w /dev/fd/2 ] tests if file descriptor 2 is writable.
2015             Note that some special rules are applied (courtesy of POSIX) if
2016             the number of arguments to test or [ ... ] is less than five: if
2017             leading ‘!’ arguments can be stripped such that only one argument
2018             remains then a string length test is performed (again, even if
2019             the argument is a unary operator); if leading ‘!’ arguments can
2020             be stripped such that three arguments remain and the second argu‐
2021             ment is a binary operator, then the binary operation is performed
2022             (even if the first argument is a unary operator, including an un‐
2023             stripped ‘!’).
2025             Note: A common mistake is to use “if [ $foo = bar ]” which fails
2026             if parameter “foo” is NULL or unset, if it has embedded spaces
2027             (i.e. IFS characters), or if it is a unary operator like ‘!’ or
2028-n’.  Use tests like “if [ "X$foo" = Xbar ]” instead.
2030     time [-p] [pipeline]
2031             If a pipeline is given, the times used to execute the pipeline
2032             are reported.  If no pipeline is given, then the user and system
2033             time used by the shell itself, and all the commands it has run
2034             since it was started, are reported.  The times reported are the
2035             real time (elapsed time from start to finish), the user CPU time
2036             (time spent running in user mode), and the system CPU time (time
2037             spent running in kernel mode).  Times are reported to standard
2038             error; the format of the output is:
2040                   0m0.00s real     0m0.00s user     0m0.00s system
2042             If the -p option is given the output is slightly longer:
2044                   real     0.00
2045                   user     0.00
2046                   sys      0.00
2048             It is an error to specify the -p option unless pipeline is a sim‐
2049             ple command.
2051             Simple redirections of standard error do not affect the output of
2052             the time command:
2054                   $ time sleep 1 2> afile
2055                   $ { time sleep 1; } 2> afile
2057             Times for the first command do not go to “afile”, but those of
2058             the second command do.
2060     times   Print the accumulated user and system times used both by the
2061             shell and by processes that the shell started which have exited.
2062             The format of the output is:
2064                   0m0.00s 0m0.00s
2065                   0m0.00s 0m0.00s
2067     trap [handler signal ...]
2068             Sets a trap handler that is to be executed when any of the speci‐
2069             fied signals are received.  handler is either a NULL string, in‐
2070             dicating the signals are to be ignored, a minus sign (‘-’), indi‐
2071             cating that the default action is to be taken for the signals
2072             (see signal(3)), or a string containing shell commands to be
2073             evaluated and executed at the first opportunity (i.e. when the
2074             current command completes, or before printing the next PS1
2075             prompt) after receipt of one of the signals.  signal is the name
2076             of a signal (e.g. PIPE or ALRM) or the number of the signal (see
2077             the kill -l command above).
2079             There are two special signals: EXIT (also known as 0), which is
2080             executed when the shell is about to exit, and ERR, which is exe‐
2081             cuted after an error occurs (an error is something that would
2082             cause the shell to exit if the -e or errexit option were set -
2083             see the set command above).  EXIT handlers are executed in the
2084             environment of the last executed command.  Note that for non-in‐
2085             teractive shells, the trap handler cannot be changed for signals
2086             that were ignored when the shell started.
2088             With no arguments, trap lists, as a series of trap commands, the
2089             current state of the traps that have been set since the shell
2090             started.  Note that the output of trap cannot be usefully piped
2091             to another process (an artifact of the fact that traps are
2092             cleared when subprocesses are created).
2094             The original Korn shell's DEBUG trap and the handling of ERR and
2095             EXIT traps in functions are not yet implemented.
2097     true    A command that exits with a zero value.
2099     type    Short form of command -V (see above).
2101     typeset [[+-lprtUux] [-L[n]] [-R[n]] [-Z[n]] [-i[n]] | -f [-tux]] [name
2102             [=value] ...]
2103             Display or set parameter attributes.  With no name arguments, pa‐
2104             rameter attributes are displayed; if no options are used, the
2105             current attributes of all parameters are printed as typeset com‐
2106             mands; if an option is given (or ‘-’ with no option letter), all
2107             parameters and their values with the specified attributes are
2108             printed; if options are introduced with ‘+’, parameter values are
2109             not printed.
2111             If name arguments are given, the attributes of the named parame‐
2112             ters are set (-) or cleared (+).  Values for parameters may op‐
2113             tionally be specified.  If typeset is used inside a function, any
2114             newly created parameters are local to the function.
2116             When -f is used, typeset operates on the attributes of functions.
2117             As with parameters, if no name arguments are given, functions are
2118             listed with their values (i.e. definitions) unless options are
2119             introduced with ‘+’, in which case only the function names are
2120             reported.
2122             -f      Function mode.  Display or set functions and their at‐
2123                     tributes, instead of parameters.
2125             -i[n]   Integer attribute.  n specifies the base to use when dis‐
2126                     playing the integer (if not specified, the base given in
2127                     the first assignment is used).  Parameters with this at‐
2128                     tribute may be assigned values containing arithmetic ex‐
2129                     pressions.
2131             -L[n]   Left justify attribute.  n specifies the field width.  If
2132                     n is not specified, the current width of a parameter (or
2133                     the width of its first assigned value) is used.  Leading
2134                     whitespace (and zeros, if used with the -Z option) is
2135                     stripped.  If necessary, values are either truncated or
2136                     space padded to fit the field width.
2138             -l      Lower case attribute.  All upper case characters in val‐
2139                     ues are converted to lower case.  (In the original Korn
2140                     shell, this parameter meant “long integer” when used with
2141                     the -i option.)
2143             -p      Print complete typeset commands that can be used to re-
2144                     create the attributes (but not the values) of parameters.
2145                     This is the default action (option exists for ksh93 com‐
2146                     patibility).
2148             -R[n]   Right justify attribute.  n specifies the field width.
2149                     If n is not specified, the current width of a parameter
2150                     (or the width of its first assigned value) is used.
2151                     Trailing whitespace is stripped.  If necessary, values
2152                     are either stripped of leading characters or space padded
2153                     to make them fit the field width.
2155             -r      Read-only attribute.  Parameters with this attribute may
2156                     not be assigned to or unset.  Once this attribute is set,
2157                     it cannot be turned off.
2159             -t      Tag attribute.  Has no meaning to the shell; provided for
2160                     application use.
2162                     For functions, -t is the trace attribute.  When functions
2163                     with the trace attribute are executed, the xtrace (-x)
2164                     shell option is temporarily turned on.
2166             -U      Unsigned integer attribute.  Integers are printed as un‐
2167                     signed values (only useful when combined with the -i op‐
2168                     tion).  This option is not in the original Korn shell.
2170             -u      Upper case attribute.  All lower case characters in val‐
2171                     ues are converted to upper case.  (In the original Korn
2172                     shell, this parameter meant “unsigned integer” when used
2173                     with the -i option, which meant upper case letters would
2174                     never be used for bases greater than 10.  See the -U op‐
2175                     tion.)
2177                     For functions, -u is the undefined attribute.  See
2178                     Functions above for the implications of this.
2180             -x      Export attribute.  Parameters (or functions) are placed
2181                     in the environment of any executed commands.  Exported
2182                     functions are not yet implemented.
2184             -Z[n]   Zero fill attribute.  If not combined with -L, this is
2185                     the same as -R, except zero padding is used instead of
2186                     space padding.
2188     ulimit [-acdfHlmnpSst [value]] ...
2189             Display or set process limits.  If no options are used, the file
2190             size limit (-f) is assumed.  value, if specified, may be either
2191             an arithmetic expression starting with a number or the word
2192             “unlimited”.  The limits affect the shell and any processes cre‐
2193             ated by the shell after a limit is imposed; limits may not be in‐
2194             creased once they are set.
2196             -a     Display all limits; unless -H is used, soft limits are
2197                    displayed.
2199             -c n   Impose a size limit of n blocks on the size of core dumps.
2201             -d n   Impose a size limit of n kilobytes on the size of the data
2202                    area.
2204             -f n   Impose a size limit of n blocks on files written by the
2205                    shell and its child processes (files of any size may be
2206                    read).
2208             -H     Set the hard limit only (the default is to set both hard
2209                    and soft limits).
2211             -l n   Impose a limit of n kilobytes on the amount of locked
2212                    (wired) physical memory.
2214             -m n   Impose a limit of n kilobytes on the amount of physical
2215                    memory used.  This limit is not enforced.
2217             -n n   Impose a limit of n file descriptors that can be open at
2218                    once.
2220             -p n   Impose a limit of n processes that can be run by the user
2221                    at any one time.
2223             -S     Set the soft limit only (the default is to set both hard
2224                    and soft limits).
2226             -s n   Impose a size limit of n kilobytes on the size of the
2227                    stack area.
2229             -t n   Impose a time limit of n CPU seconds spent in user mode to
2230                    be used by each process.
2232             As far as ulimit is concerned, a block is 512 bytes.
2234     umask [-S] [mask]
2235             Display or set the file permission creation mask, or umask (see
2236             umask(2)).  If the -S option is used, the mask displayed or set
2237             is symbolic; otherwise, it is an octal number.
2239             Symbolic masks are like those used by chmod(1).  When used, they
2240             describe what permissions may be made available (as opposed to
2241             octal masks in which a set bit means the corresponding bit is to
2242             be cleared).  For example, “ug=rwx,o=” sets the mask so files
2243             will not be readable, writable, or executable by “others”, and is
2244             equivalent (on most systems) to the octal mask “007”.
2246     unalias [-adt] [name ...]
2247             The aliases for the given names are removed.  If the -a option is
2248             used, all aliases are removed.  If the -t or -d options are used,
2249             the indicated operations are carried out on tracked or directory
2250             aliases, respectively.
2252     unset [-fv] parameter ...
2253             Unset the named parameters (-v, the default) or functions (-f).
2254             The exit status is non-zero if any of the parameters have the
2255             read-only attribute set, zero otherwise.
2257     wait [job ...]
2258             Wait for the specified job(s) to finish.  The exit status of wait
2259             is that of the last specified job; if the last job is killed by a
2260             signal, the exit status is 128 + the number of the signal (see
2261             kill -l exit-status above); if the last specified job can't be
2262             found (because it never existed, or had already finished), the
2263             exit status of wait is 127.  See Job control below for the format
2264             of job.  wait will return if a signal for which a trap has been
2265             set is received, or if a SIGHUP, SIGINT, or SIGQUIT signal is re‐
2266             ceived.
2268             If no jobs are specified, wait waits for all currently running
2269             jobs (if any) to finish and exits with a zero status.  If job
2270             monitoring is enabled, the completion status of jobs is printed
2271             (this is not the case when jobs are explicitly specified).
2273     whence [-pv] [name ...]
2274             For each name, the type of command is listed (reserved word,
2275             built-in, alias, function, tracked alias, or executable).  If the
2276             -p option is used, a path search is performed even if name is a
2277             reserved word, alias, etc.  Without the -v option, whence is sim‐
2278             ilar to command -v except that whence won't print aliases as
2279             alias commands.  With the -v option, whence is the same as
2280             command -V.  Note that for whence, the -p option does not affect
2281             the search path used, as it does for command.  If the type of one
2282             or more of the names could not be determined, the exit status is
2283             non-zero.
2285   Job control
2286     Job control refers to the shell's ability to monitor and control jobs,
2287     which are processes or groups of processes created for commands or pipe‐
2288     lines.  At a minimum, the shell keeps track of the status of the back‐
2289     ground (i.e. asynchronous) jobs that currently exist; this information
2290     can be displayed using the jobs commands.  If job control is fully en‐
2291     abled (using set -m or set -o monitor), as it is for interactive shells,
2292     the processes of a job are placed in their own process group.  Foreground
2293     jobs can be stopped by typing the suspend character from the terminal
2294     (normally ^Z), jobs can be restarted in either the foreground or back‐
2295     ground using the fg and bg commands, and the state of the terminal is
2296     saved or restored when a foreground job is stopped or restarted, respec‐
2297     tively.
2299     Note that only commands that create processes (e.g. asynchronous com‐
2300     mands, subshell commands, and non-built-in, non-function commands) can be
2301     stopped; commands like read cannot be.
2303     When a job is created, it is assigned a job number.  For interactive
2304     shells, this number is printed inside “[..]”, followed by the process IDs
2305     of the processes in the job when an asynchronous command is run.  A job
2306     may be referred to in the bg, fg, jobs, kill, and wait commands either by
2307     the process ID of the last process in the command pipeline (as stored in
2308     the $! parameter) or by prefixing the job number with a percent sign
2309     (‘%’).  Other percent sequences can also be used to refer to jobs:
2311     %+ | %% | %    The most recently stopped job or, if there are no stopped
2312                    jobs, the oldest running job.
2314     %-             The job that would be the %+ job if the latter did not ex‐
2315                    ist.
2317     %n             The job with job number n.
2319     %?string       The job with its command containing the string string (an
2320                    error occurs if multiple jobs are matched).
2322     %string        The job with its command starting with the string string
2323                    (an error occurs if multiple jobs are matched).
2325     When a job changes state (e.g. a background job finishes or foreground
2326     job is stopped), the shell prints the following status information:
2328           [number] flag status command
2330     where...
2332     number   is the job number of the job;
2334     flag     is the ‘+’ or ‘-’ character if the job is the %+ or %- job, re‐
2335              spectively, or space if it is neither;
2337     status   indicates the current state of the job and can be:
2339              Done [number]
2340                         The job exited.  number is the exit status of the
2341                         job, which is omitted if the status is zero.
2343              Running    The job has neither stopped nor exited (note that
2344                         running does not necessarily mean consuming CPU time
2345                         - the process could be blocked waiting for some
2346                         event).
2348              Stopped [signal]
2349                         The job was stopped by the indicated signal (if no
2350                         signal is given, the job was stopped by SIGTSTP).
2352              signal-description [“core dumped”]
2353                         The job was killed by a signal (e.g. memory fault,
2354                         hangup); use kill -l for a list of signal descrip‐
2355                         tions.  The “core dumped” message indicates the
2356                         process created a core file.
2358     command  is the command that created the process.  If there are multiple
2359              processes in the job, each process will have a line showing its
2360              command and possibly its status, if it is different from the
2361              status of the previous process.
2363     When an attempt is made to exit the shell while there are jobs in the
2364     stopped state, the shell warns the user that there are stopped jobs and
2365     does not exit.  If another attempt is immediately made to exit the shell,
2366     the stopped jobs are sent a SIGHUP signal and the shell exits.  Simi‐
2367     larly, if the nohup option is not set and there are running jobs when an
2368     attempt is made to exit a login shell, the shell warns the user and does
2369     not exit.  If another attempt is immediately made to exit the shell, the
2370     running jobs are sent a SIGHUP signal and the shell exits.
2372   Interactive input line editing
2373     The shell supports three modes of reading command lines from a tty(4) in
2374     an interactive session, controlled by the emacs, gmacs, and vi options
2375     (at most one of these can be set at once).  The default is emacs.  Edit‐
2376     ing modes can be set explicitly using the set built-in, or implicitly via
2377     the EDITOR and VISUAL environment variables.  If none of these options
2378     are enabled, the shell simply reads lines using the normal tty(4) driver.
2379     If the emacs or gmacs option is set, the shell allows emacs-like editing
2380     of the command; similarly, if the vi option is set, the shell allows vi-
2381     like editing of the command.  These modes are described in detail in the
2382     following sections.
2384     In these editing modes, if a line is longer than the screen width (see
2385     the COLUMNS parameter), a ‘>’, ‘+’, or ‘<’ character is displayed in the
2386     last column indicating that there are more characters after, before and
2387     after, or before the current position, respectively.  The line is
2388     scrolled horizontally as necessary.
2390   Emacs editing mode
2391     When the emacs option is set, interactive input line editing is enabled.
2392     Warning: This mode is slightly different from the emacs mode in the orig‐
2393     inal Korn shell.  In this mode, various editing commands (typically bound
2394     to one or more control characters) cause immediate actions without wait‐
2395     ing for a newline.  Several editing commands are bound to particular con‐
2396     trol characters when the shell is invoked; these bindings can be changed
2397     using the bind command.
2399     The following is a list of available editing commands.  Each description
2400     starts with the name of the command, suffixed with a colon; an [n] (if
2401     the command can be prefixed with a count); and any keys the command is
2402     bound to by default, written using caret notation e.g. the ASCII ESC
2403     character is written as ^[.  ^[A-Z] sequences are not case sensitive.  A
2404     count prefix for a command is entered using the sequence ^[n, where n is
2405     a sequence of 1 or more digits.  Unless otherwise specified, if a count
2406     is omitted, it defaults to 1.
2408     Note that editing command names are used only with the bind command.
2409     Furthermore, many editing commands are useful only on terminals with a
2410     visible cursor.  The default bindings were chosen to resemble correspond‐
2411     ing Emacs key bindings.  The user's tty(4) characters (e.g. ERASE) are
2412     bound to reasonable substitutes and override the default bindings.
2414     abort: ^C, ^G
2415             Useful as a response to a request for a search-history pattern in
2416             order to abort the search.
2418     auto-insert: [n]
2419             Simply causes the character to appear as literal input.  Most or‐
2420             dinary characters are bound to this.
2422     backward-char: [n] ^B, ^X^D
2423             Moves the cursor backward n characters.
2425     backward-word: [n] ^[b
2426             Moves the cursor backward to the beginning of the word; words
2427             consist of alphanumerics, underscore (‘_’), and dollar sign (‘$’)
2428             characters.
2430     beginning-of-history: ^[<
2431             Moves to the beginning of the history.
2433     beginning-of-line: ^A
2434             Moves the cursor to the beginning of the edited input line.
2436     capitalize-word: [n] ^[C, ^[c
2437             Uppercase the first character in the next n words, leaving the
2438             cursor past the end of the last word.
2440     clear-screen: ^L
2441             Clears the screen if the TERM parameter is set and the terminal
2442             supports clearing the screen, then reprints the prompt string and
2443             the current input line.
2445     comment: ^[#
2446             If the current line does not begin with a comment character, one
2447             is added at the beginning of the line and the line is entered (as
2448             if return had been pressed); otherwise, the existing comment
2449             characters are removed and the cursor is placed at the beginning
2450             of the line.
2452     complete: ^[^[
2453             Automatically completes as much as is unique of the command name
2454             or the file name containing the cursor.  If the entire remaining
2455             command or file name is unique, a space is printed after its com‐
2456             pletion, unless it is a directory name in which case ‘/’ is ap‐
2457             pended.  If there is no command or file name with the current
2458             partial word as its prefix, a bell character is output (usually
2459             causing a beep to be sounded).
2461             Custom completions may be configured by creating an array named
2462             ‘complete_command’, optionally suffixed with an argument number
2463             to complete only for a single argument.  So defining an array
2464             named ‘complete_kill’ provides possible completions for any argu‐
2465             ment to the kill(1) command, but ‘complete_kill_1’ only completes
2466             the first argument.  For example, the following command makes
2467             oksh offer a selection of signal names for the first argument to
2468             kill(1):
2470                   set -A complete_kill_1 -- -9 -HUP -INFO -KILL -TERM
2472     complete-command: ^X^[
2473             Automatically completes as much as is unique of the command name
2474             having the partial word up to the cursor as its prefix, as in the
2475             complete command above.
2477     complete-file: ^[^X
2478             Automatically completes as much as is unique of the file name
2479             having the partial word up to the cursor as its prefix, as in the
2480             complete command described above.
2482     complete-list: ^I, ^[=
2483             Complete as much as is possible of the current word, and list the
2484             possible completions for it.  If only one completion is possible,
2485             match as in the complete command above.
2487     delete-char-backward: [n] ERASE, ^?, ^H
2488             Deletes n characters before the cursor.
2490     delete-char-forward: [n] Delete
2491             Deletes n characters after the cursor.
2493     delete-word-backward: [n] WERASE, ^[ERASE, ^W, ^[^?, ^[^H, ^[h
2494             Deletes n words before the cursor.
2496     delete-word-forward: [n] ^[d
2497             Deletes n words after the cursor.
2499     down-history: [n] ^N, ^XB
2500             Scrolls the history buffer forward n lines (later).  Each input
2501             line originally starts just after the last entry in the history
2502             buffer, so down-history is not useful until either search-history
2503             or up-history has been performed.
2505     downcase-word: [n] ^[L, ^[l
2506             Lowercases the next n words.
2508     end-of-history: ^[>
2509             Moves to the end of the history.
2511     end-of-line: ^E
2512             Moves the cursor to the end of the input line.
2514     eot: ^_
2515             Acts as an end-of-file; this is useful because edit-mode input
2516             disables normal terminal input canonicalization.
2518     eot-or-delete: [n] ^D
2519             Acts as eot if alone on a line; otherwise acts as
2520             delete-char-forward.
2522     error:  Error (ring the bell).
2524     exchange-point-and-mark: ^X^X
2525             Places the cursor where the mark is and sets the mark to where
2526             the cursor was.
2528     expand-file: ^[*
2529             Appends a ‘*’ to the current word and replaces the word with the
2530             result of performing file globbing on the word.  If no files
2531             match the pattern, the bell is rung.
2533     forward-char: [n] ^F, ^XC
2534             Moves the cursor forward n characters.
2536     forward-word: [n] ^[f
2537             Moves the cursor forward to the end of the nth word.
2539     goto-history: [n] ^[g
2540             Goes to history number n.
2542     kill-line: KILL
2543             Deletes the entire input line.
2545     kill-to-eol: [n] ^K
2546             Deletes the input from the cursor to the end of the line if n is
2547             not specified; otherwise deletes characters between the cursor
2548             and column n.
2550     list: ^[?
2551             Prints a sorted, columnated list of command names or file names
2552             (if any) that can complete the partial word containing the cur‐
2553             sor.  Directory names have ‘/’ appended to them.
2555     list-command: ^X?
2556             Prints a sorted, columnated list of command names (if any) that
2557             can complete the partial word containing the cursor.
2559     list-file: ^X^Y
2560             Prints a sorted, columnated list of file names (if any) that can
2561             complete the partial word containing the cursor.  File type indi‐
2562             cators are appended as described under list above.
2564     newline: ^J, ^M
2565             Causes the current input line to be processed by the shell.  The
2566             current cursor position may be anywhere on the line.
2568     newline-and-next: ^O
2569             Causes the current input line to be processed by the shell, and
2570             the next line from history becomes the current line.  This is
2571             only useful after an up-history or search-history.
2573     no-op: QUIT
2574             This does nothing.
2576     prev-hist-word: [n] ^[., ^[_
2577             The last (nth) word of the previous command is inserted at the
2578             cursor.
2580     quote: ^^
2581             The following character is taken literally rather than as an
2582             editing command.
2584     redraw:
2585             Reprints the prompt string and the current input line.
2587     search-character-backward: [n] ^[^]
2588             Search backward in the current line for the nth occurrence of the
2589             next character typed.
2591     search-character-forward: [n] ^]
2592             Search forward in the current line for the nth occurrence of the
2593             next character typed.
2595     search-history: ^R
2596             Enter incremental search mode.  The internal history list is
2597             searched backwards for commands matching the input.  An initial
2598             ‘^’ in the search string anchors the search.  The abort key will
2599             leave search mode.  Other commands will be executed after leaving
2600             search mode.  Successive search-history commands continue search‐
2601             ing backward to the next previous occurrence of the pattern.  The
2602             history buffer retains only a finite number of lines; the oldest
2603             are discarded as necessary.
2605     set-mark-command: ^[⟨space⟩
2606             Set the mark at the cursor position.
2608     transpose-chars: ^T
2609             If at the end of line, or if the gmacs option is set, this ex‐
2610             changes the two previous characters; otherwise, it exchanges the
2611             previous and current characters and moves the cursor one charac‐
2612             ter to the right.
2614     up-history: [n] ^P, ^XA
2615             Scrolls the history buffer backward n lines (earlier).
2617     upcase-word: [n] ^[U, ^[u
2618             Uppercase the next n words.
2620     quote: ^V
2621             Synonym for ^^.
2623     yank: ^Y
2624             Inserts the most recently killed text string at the current cur‐
2625             sor position.
2627     yank-pop: ^[y
2628             Immediately after a yank, replaces the inserted text string with
2629             the next previously killed text string.
2631     The following editing commands lack default bindings but can be used with
2632     the bind command:
2634     kill-region
2635             Deletes the input between the cursor and the mark.
2637   Vi editing mode
2638     The vi command-line editor in oksh has basically the same commands as the
2639     vi(1) editor with the following exceptions:
2641     You start out in insert mode.
2643     There are file name and command completion commands: =, \, *, ^X, ^E,
2644         ^F, and, optionally, ⟨tab⟩ and ⟨esc⟩.
2646     The _ command is different (in oksh it is the last argument command;
2647         in vi(1) it goes to the start of the current line).
2649     The / and G commands move in the opposite direction to the j command.
2651     Commands which don't make sense in a single line editor are not
2652         available (e.g. screen movement commands and ex(1)-style colon (:)
2653         commands).
2655     Note that the ^X stands for control-X; also ⟨esc⟩, ⟨space⟩, and ⟨tab⟩ are
2656     used for escape, space, and tab, respectively (no kidding).
2658     Like vi(1), there are two modes: “insert” mode and “command” mode.  In
2659     insert mode, most characters are simply put in the buffer at the current
2660     cursor position as they are typed; however, some characters are treated
2661     specially.  In particular, the following characters are taken from cur‐
2662     rent tty(4) settings (see stty(1)) and have their usual meaning (normal
2663     values are in parentheses): kill (^U), erase (^?), werase (^W), eof (^D),
2664     intr (^C), and quit (^\).  In addition to the above, the following char‐
2665     acters are also treated specially in insert mode:
2667     ^E          Command and file name enumeration (see below).
2669     ^F          Command and file name completion (see below).  If used twice
2670                 in a row, the list of possible completions is displayed; if
2671                 used a third time, the completion is undone.
2673     ^H          Erases previous character.
2675     ^J | ^M     End of line.  The current line is read, parsed, and executed
2676                 by the shell.
2678     ^V          Literal next.  The next character typed is not treated spe‐
2679                 cially (can be used to insert the characters being described
2680                 here).
2682     ^X          Command and file name expansion (see below).
2684     ⟨esc⟩       Puts the editor in command mode (see below).
2686     ⟨tab⟩       Optional file name and command completion (see ^F above), en‐
2687                 abled with set -o vi-tabcomplete.
2689     In command mode, each character is interpreted as a command.  Characters
2690     that don't correspond to commands, are illegal combinations of commands,
2691     or are commands that can't be carried out, all cause beeps.  In the fol‐
2692     lowing command descriptions, an [n] indicates the command may be prefixed
2693     by a number (e.g. 10l moves right 10 characters); if no number prefix is
2694     used, n is assumed to be 1 unless otherwise specified.  The term “current
2695     position” refers to the position between the cursor and the character
2696     preceding the cursor.  A “word” is a sequence of letters, digits, and un‐
2697     derscore characters or a sequence of non-letter, non-digit, non-under‐
2698     score, and non-whitespace characters (e.g. “ab2*&^” contains two words)
2699     and a “big-word” is a sequence of non-whitespace characters.
2701     Special oksh vi commands:
2703     The following commands are not in, or are different from, the normal vi
2704     file editor:
2706     [n]_        Insert a space followed by the nth big-word from the last
2707                 command in the history at the current position and enter in‐
2708                 sert mode; if n is not specified, the last word is inserted.
2710     #           Insert the comment character (‘#’) at the start of the cur‐
2711                 rent line and return the line to the shell (equivalent to
2712                 I#^J).
2714     [n]g        Like G, except if n is not specified, it goes to the most re‐
2715                 cent remembered line.
2717     [n]v        Edit line n using the vi(1) editor; if n is not specified,
2718                 the current line is edited.  The actual command executed is
2719                 fc -e ${VISUAL:-${EDITOR:-vi}} n.
2721     * and ^X    Command or file name expansion is applied to the current big-
2722                 word (with an appended ‘*’ if the word contains no file glob‐
2723                 bing characters) - the big-word is replaced with the result‐
2724                 ing words.  If the current big-word is the first on the line
2725                 or follows one of the characters ‘;’, ‘|’, ‘&’, ‘(’, or ‘)’,
2726                 and does not contain a slash (‘/’), then command expansion is
2727                 done; otherwise file name expansion is done.  Command expan‐
2728                 sion will match the big-word against all aliases, functions,
2729                 and built-in commands as well as any executable files found
2730                 by searching the directories in the PATH parameter.  File
2731                 name expansion matches the big-word against the files in the
2732                 current directory.  After expansion, the cursor is placed
2733                 just past the last word and the editor is in insert mode.
2735     [n]\, [n]^F, [n]⟨tab⟩, and [n]⟨esc⟩
2736                 Command/file name completion.  Replace the current big-word
2737                 with the longest unique match obtained after performing com‐
2738                 mand and file name expansion.  ⟨tab⟩ is only recognized if
2739                 the vi-tabcomplete option is set, while ⟨esc⟩ is only recog‐
2740                 nized if the vi-esccomplete option is set (see set -o).  If n
2741                 is specified, the nth possible completion is selected (as re‐
2742                 ported by the command/file name enumeration command).
2744     = and ^E    Command/file name enumeration.  List all the commands or
2745                 files that match the current big-word.
2747     @c          Macro expansion.  Execute the commands found in the alias _c.
2749     Intra-line movement commands:
2751     [n]h and [n]^H
2752             Move left n characters.
2754     [n]l and [n]⟨space⟩
2755             Move right n characters.
2757     0       Move to column 0.
2759     ^       Move to the first non-whitespace character.
2761     [n]|    Move to column n.
2763     $       Move to the last character.
2765     [n]b    Move back n words.
2767     [n]B    Move back n big-words.
2769     [n]e    Move forward to the end of the word, n times.
2771     [n]E    Move forward to the end of the big-word, n times.
2773     [n]w    Move forward n words.
2775     [n]W    Move forward n big-words.
2777     %       Find match.  The editor looks forward for the nearest parenthe‐
2778             sis, bracket, or brace and then moves the cursor to the matching
2779             parenthesis, bracket, or brace.
2781     [n]fc   Move forward to the nth occurrence of the character c.
2783     [n]Fc   Move backward to the nth occurrence of the character c.
2785     [n]tc   Move forward to just before the nth occurrence of the character
2786             c.
2788     [n]Tc   Move backward to just before the nth occurrence of the character
2789             c.
2791     [n];    Repeats the last f, F, t, or T command.
2793     [n],    Repeats the last f, F, t, or T command, but moves in the opposite
2794             direction.
2796     Inter-line movement commands:
2798     [n]j, [n]+, and [n]^N
2799             Move to the nth next line in the history.
2801     [n]k, [n]-, and [n]^P
2802             Move to the nth previous line in the history.
2804     [n]G    Move to line n in the history; if n is not specified, the number
2805             of the first remembered line is used.
2807     [n]g    Like G, except if n is not specified, it goes to the most recent
2808             remembered line.
2810     [n]/string
2811             Search backward through the history for the nth line containing
2812             string; if string starts with ‘^’, the remainder of the string
2813             must appear at the start of the history line for it to match.
2815     [n]?string
2816             Same as /, except it searches forward through the history.
2818     [n]n    Search for the nth occurrence of the last search string; the di‐
2819             rection of the search is the same as the last search.
2821     [n]N    Search for the nth occurrence of the last search string; the di‐
2822             rection of the search is the opposite of the last search.
2824     Edit commands
2826     [n]a    Append text n times; goes into insert mode just after the current
2827             position.  The append is only replicated if command mode is re-
2828             entered i.e. ⟨esc⟩ is used.
2830     [n]A    Same as a, except it appends at the end of the line.
2832     [n]i    Insert text n times; goes into insert mode at the current posi‐
2833             tion.  The insertion is only replicated if command mode is re-en‐
2834             tered i.e. ⟨esc⟩ is used.
2836     [n]I    Same as i, except the insertion is done just before the first
2837             non-blank character.
2839     [n]s    Substitute the next n characters (i.e. delete the characters and
2840             go into insert mode).
2842     S       Substitute whole line.  All characters from the first non-blank
2843             character to the end of the line are deleted and insert mode is
2844             entered.
2846     [n]cmove-cmd
2847             Change from the current position to the position resulting from n
2848             move-cmds (i.e. delete the indicated region and go into insert
2849             mode); if move-cmd is c, the line starting from the first non-
2850             blank character is changed.
2852     C       Change from the current position to the end of the line (i.e.
2853             delete to the end of the line and go into insert mode).
2855     [n]x    Delete the next n characters.
2857     [n]X    Delete the previous n characters.
2859     D       Delete to the end of the line.
2861     [n]dmove-cmd
2862             Delete from the current position to the position resulting from n
2863             move-cmds; move-cmd is a movement command (see above) or d, in
2864             which case the current line is deleted.
2866     [n]rc   Replace the next n characters with the character c.
2868     [n]R    Replace.  Enter insert mode but overwrite existing characters in‐
2869             stead of inserting before existing characters.  The replacement
2870             is repeated n times.
2872     [n]~    Change the case of the next n characters.
2874     [n]ymove-cmd
2875             Yank from the current position to the position resulting from n
2876             move-cmds into the yank buffer; if move-cmd is y, the whole line
2877             is yanked.
2879     Y       Yank from the current position to the end of the line.
2881     [n]p    Paste the contents of the yank buffer just after the current po‐
2882             sition, n times.
2884     [n]P    Same as p, except the buffer is pasted at the current position.
2886     Miscellaneous vi commands
2888     ^J and ^M
2889             The current line is read, parsed, and executed by the shell.
2891     ^L and ^R
2892             Redraw the current line.
2894     [n].    Redo the last edit command n times.
2896     u       Undo the last edit command.
2898     U       Undo all changes that have been made to the current line.
2900     intr and quit
2901             The interrupt and quit terminal characters cause the current line
2902             to be deleted and a new prompt to be printed.


2905     ~/.profile           User's login profile.
2906     /etc/ksh.kshrc       Global configuration file.  Not sourced by default.
2907     /etc/profile         System login profile.
2908     /etc/shells          Shell database.
2909     /etc/suid_profile    Privileged shell profile.


2912     csh(1), ed(1), mg(1), sh(1), stty(1), vi(1), shells(5), environ(7),
2913     script(7)
2915     Morris Bolsky and David Korn, The KornShell Command and Programming
2916     Language, 2nd Edition, Prentice Hall, 1995, ISBN 0131827006.
2918     Stephen G. Kochan and Patrick H. Wood, UNIX Shell Programming, 3rd
2919     Edition, Sams, 2003, ISBN 0672324903.
2921     IEEE Inc., IEEE Standard for Information Technology - Portable Operating
2922     System Interface (POSIX) - Part 2: Shell and Utilities, 1993, ISBN
2923     1-55937-266-9.


2926     This page documents version @(#)PD KSH v5.2.14 99/07/13.2 of the public
2927     domain Korn shell.


2930     This shell is based on the public domain 7th edition Bourne shell clone
2931     by Charles Forsyth and parts of the BRL shell by Doug A. Gwyn, Doug
2932     Kingston, Ron Natalie, Arnold Robbins, Lou Salkind, and others.  The
2933     first release of pdksh was created by Eric Gisin, and it was subsequently
2934     maintained by John R. MacMillan <change!john@sq.sq.com>, Simon J. Gerraty
2935     <sjg@zen.void.oz.au>, and Michael Rendell <michael@cs.mun.ca>.  The
2936     CONTRIBUTORS file in the source distribution contains a more complete
2937     list of people and their part in the shell's development.


2940     $(command) expressions are currently parsed by finding the closest match‐
2941     ing (unquoted) parenthesis.  Thus constructs inside $(command) may pro‐
2942     duce an error.  For example, the parenthesis in ‘x);;’ is interpreted as
2943     the closing parenthesis in ‘$(case x in x);; *);; esac)’.
2945BSD                              April 3, 2019                             BSD