1SH(1P) POSIX Programmer's Manual SH(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 sh - shell, the standard command language interpreter
13
15 sh [-abCefhimnuvx][-o option][+abCefhimnuvx][+o option]
16 [command_file [argument...]]
17 sh -c[-abCefhimnuvx][-o option][+abCefhimnuvx][+o option]command_string
19 [command_name [argument...]]
20 sh -s[-abCefhimnuvx][-o option][+abCefhimnuvx][+o option][argument]
22
25 The sh utility is a command language interpreter that shall execute
26 commands read from a command line string, the standard input, or a
27 specified file. The application shall ensure that the commands to be
28 executed are expressed in the language described in Shell Command Lan‐
29 guage .
30 Pathname expansion shall not fail due to the size of a file.
32 Shell input and output redirections have an implementation-defined off‐
34 set maximum that is established in the open file description.
35
37 The sh utility shall conform to the Base Definitions volume of
38 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines, with an
39 extension for support of a leading plus sign ( '+' ) as noted below.
40 The -a, -b, -C, -e, -f, -m, -n, -o option, -u, -v, and -x options are
42 described as part of the set utility in Special Built-In Utilities .
43 The option letters derived from the set special built-in shall also be
44 accepted with a leading plus sign ( '+' ) instead of a leading hyphen
45 (meaning the reverse case of the option as described in this volume of
46 IEEE Std 1003.1-2001).
47 The following additional options shall be supported:
49 -c Read commands from the command_string operand. Set the value of
51 special parameter 0 (see Special Parameters ) from the value of
52 the command_name operand and the positional parameters ($1, $2,
53 and so on) in sequence from the remaining argument operands. No
54 commands shall be read from the standard input.
55 -i Specify that the shell is interactive; see below. An implementa‐
57 tion may treat specifying the -i option as an error if the real
58 user ID of the calling process does not equal the effective user
59 ID or if the real group ID does not equal the effective group
60 ID.
61 -s Read commands from the standard input.
63 If there are no operands and the -c option is not specified, the -s
66 option shall be assumed.
67 If the -i option is present, or if there are no operands and the
69 shell's standard input and standard error are attached to a terminal,
70 the shell is considered to be interactive.
71
73 The following operands shall be supported:
74 - A single hyphen shall be treated as the first operand and then
76 ignored. If both '-' and "--" are given as arguments, or if
77 other operands precede the single hyphen, the results are unde‐
78 fined.
79 argument
81 The positional parameters ($1, $2, and so on) shall be set to
82 arguments, if any.
83 command_file
85 The pathname of a file containing commands. If the pathname con‐
86 tains one or more slash characters, the implementation attempts
87 to read that file; the file need not be executable. If the path‐
88 name does not contain a slash character:
89 * The implementation shall attempt to read that file from the
91 current working directory; the file need not be executable.
92 * If the file is not in the current working directory, the
94 implementation may perform a search for an executable file
95 using the value of PATH, as described in Command Search and
96 Execution .
97 Special parameter 0 (see Special Parameters ) shall be set to the value
99 of command_file. If sh is called using a synopsis form that omits com‐
100 mand_file, special parameter 0 shall be set to the value of the first
101 argument passed to sh from its parent (for example, argv[0] for a C
102 program), which is normally a pathname used to execute the sh utility.
103 command_name
105 A string assigned to special parameter 0 when executing the com‐
107 mands in command_string. If command_name is not specified, spe‐
108 cial parameter 0 shall be set to the value of the first argument
109 passed to sh from its parent (for example, argv[0] for a C pro‐
110 gram), which is normally a pathname used to execute the sh util‐
111 ity.
112 command_string
114 A string that shall be interpreted by the shell as one or more
116 commands, as if the string were the argument to the system()
117 function defined in the System Interfaces volume of
118 IEEE Std 1003.1-2001. If the command_string operand is an empty
119 string, sh shall exit with a zero exit status.
120
123 The standard input shall be used only if one of the following is true:
124 * The -s option is specified.
126 * The -c option is not specified and no operands are specified.
128 * The script executes one or more commands that require input from
130 standard input (such as a read command that does not redirect its
131 input).
132 See the INPUT FILES section.
134 When the shell is using standard input and it invokes a command that
136 also uses standard input, the shell shall ensure that the standard
137 input file pointer points directly after the command it has read when
138 the command begins execution. It shall not read ahead in such a manner
139 that any characters intended to be read by the invoked command are con‐
140 sumed by the shell (whether interpreted by the shell or not) or that
141 characters that are not read by the invoked command are not seen by the
142 shell. When the command expecting to read standard input is started
143 asynchronously by an interactive shell, it is unspecified whether char‐
144 acters are read by the command or interpreted by the shell.
145 If the standard input to sh is a FIFO or terminal device and is set to
147 non-blocking reads, then sh shall enable blocking reads on standard
148 input. This shall remain in effect when the command completes.
149
151 The input file shall be a text file, except that line lengths shall be
152 unlimited. If the input file is empty or consists solely of blank lines
153 or comments, or both, sh shall exit with a zero exit status.
154
156 The following environment variables shall affect the execution of sh:
157 ENV This variable, when and only when an interactive shell is
159 invoked, shall be subjected to parameter expansion (see Parame‐
160 ter Expansion ) by the shell, and the resulting value shall be
161 used as a pathname of a file containing shell commands to exe‐
162 cute in the current environment. The file need not be exe‐
163 cutable. If the expanded value of ENV is not an absolute path‐
164 name, the results are unspecified. ENV shall be ignored if the
165 real and effective user IDs or real and effective group IDs of
166 the process are different.
167 FCEDIT This variable, when expanded by the shell, shall determine the
169 default value for the -e editor option's editor option-argument.
170 If FCEDIT is null or unset, ed shall be used as the editor. This
171 volume of IEEE Std 1003.1-2001 specifies the effects of this
172 variable only for systems supporting the User Portability Utili‐
173 ties option.
174 HISTFILE
176 Determine a pathname naming a command history file. If the HIST‐
177 FILE variable is not set, the shell may attempt to access or
178 create a file .sh_history in the directory referred to by the
179 HOME environment variable. If the shell cannot obtain both read
180 and write access to, or create, the history file, it shall use
181 an unspecified mechanism that allows the history to operate
182 properly. (References to history "file" in this section shall be
183 understood to mean this unspecified mechanism in such cases.) An
184 implementation may choose to access this variable only when ini‐
185 tializing the history file; this initialization shall occur when
186 fc or sh first attempt to retrieve entries from, or add entries
187 to, the file, as the result of commands issued by the user, the
188 file named by the ENV variable, or implementation-defined system
189 start-up files. Implementations may choose to disable the his‐
190 tory list mechanism for users with appropriate privileges who do
191 not set HISTFILE ; the specific circumstances under which this
192 occurs are implementation-defined. If more than one instance of
193 the shell is using the same history file, it is unspecified how
194 updates to the history file from those shells interact. As
195 entries are deleted from the history file, they shall be deleted
196 oldest first. It is unspecified when history file entries are
197 physically removed from the history file. This volume of
198 IEEE Std 1003.1-2001 specifies the effects of this variable only
199 for systems supporting the User Portability Utilities option.
200 HISTSIZE
202 Determine a decimal number representing the limit to the number
203 of previous commands that are accessible. If this variable is
204 unset, an unspecified default greater than or equal to 128 shall
205 be used. The maximum number of commands in the history list is
206 unspecified, but shall be at least 128. An implementation may
207 choose to access this variable only when initializing the his‐
208 tory file, as described under HISTFILE. Therefore, it is
209 unspecified whether changes made to HISTSIZE after the history
210 file has been initialized are effective.
211 HOME Determine the pathname of the user's home directory. The con‐
213 tents of HOME are used in tilde expansion as described in Tilde
214 Expansion . This volume of IEEE Std 1003.1-2001 specifies the
215 effects of this variable only for systems supporting the User
216 Portability Utilities option.
217 IFS (Input Field Separators.) A string treated as a list of charac‐
219 ters that shall be used for field splitting and to split lines
220 into words with the read command. See Field Splitting . If IFS
221 is not set, the shell shall behave as if the value of IFS were
222 <space>, <tab>, and <newline>. Implementations may ignore the
223 value of IFS in the environment at the time sh is invoked,
224 treating IFS as if it were not set.
225 LANG Provide a default value for the internationalization variables
227 that are unset or null. (See the Base Definitions volume of
228 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
229 ables for the precedence of internationalization variables used
230 to determine the values of locale categories.)
231 LC_ALL If set to a non-empty string value, override the values of all
233 the other internationalization variables.
234 LC_COLLATE
236 Determine the behavior of range expressions, equivalence
238 classes, and multi-character collating elements within pattern
239 matching.
240 LC_CTYPE
242 Determine the locale for the interpretation of sequences of
243 bytes of text data as characters (for example, single-byte as
244 opposed to multi-byte characters in arguments and input files),
245 which characters are defined as letters (character class alpha),
246 and the behavior of character classes within pattern matching.
247 LC_MESSAGES
249 Determine the locale that should be used to affect the format
250 and contents of diagnostic messages written to standard error.
251 MAIL Determine a pathname of the user's mailbox file for purposes of
253 incoming mail notification. If this variable is set, the shell
254 shall inform the user if the file named by the variable is cre‐
255 ated or if its modification time has changed. Informing the user
256 shall be accomplished by writing a string of unspecified format
257 to standard error prior to the writing of the next primary
258 prompt string. Such check shall be performed only after the com‐
259 pletion of the interval defined by the MAILCHECK variable after
260 the last such check. The user shall be informed only if MAIL is
261 set and MAILPATH is not set. This volume of IEEE Std 1003.1-2001
262 specifies the effects of this variable only for systems support‐
263 ing the User Portability Utilities option.
264 MAILCHECK
266 Establish a decimal integer value that specifies how often (in
268 seconds) the shell shall check for the arrival of mail in the
269 files specified by the MAILPATH or MAIL variables. The default
270 value shall be 600 seconds. If set to zero, the shell shall
271 check before issuing each primary prompt. This volume of
272 IEEE Std 1003.1-2001 specifies the effects of this variable only
273 for systems supporting the User Portability Utilities option.
274 MAILPATH
276 Provide a list of pathnames and optional messages separated by
277 colons. If this variable is set, the shell shall inform the
278 user if any of the files named by the variable are created or if
279 any of their modification times change. (See the preceding entry
280 for MAIL for descriptions of mail arrival and user informing.)
281 Each pathname can be followed by '%' and a string that shall be
282 subjected to parameter expansion and written to standard error
283 when the modification time changes. If a '%' character in the
284 pathname is preceded by a backslash, it shall be treated as a
285 literal '%' in the pathname. The default message is unspecified.
286 The MAILPATH environment variable takes precedence over the MAIL vari‐
288 able. This volume of IEEE Std 1003.1-2001 specifies the effects of this
289 variable only for systems supporting the User Portability Utilities
290 option.
291 NLSPATH
293 Determine the location of message catalogs for the processing of
294 LC_MESSAGES .
295 PATH Establish a string formatted as described in the Base Defini‐
297 tions volume of IEEE Std 1003.1-2001, Chapter 8, Environment
298 Variables, used to effect command interpretation; see Command
299 Search and Execution .
300 PWD This variable shall represent an absolute pathname of the cur‐
302 rent working directory. Assignments to this variable may be
303 ignored unless the value is an absolute pathname of the current
304 working directory and there are no filename components of dot or
305 dot-dot.
306
309 Default.
310
312 See the STDERR section.
313
315 Except as otherwise stated (by the descriptions of any invoked utili‐
316 ties or in interactive mode), standard error shall be used only for
317 diagnostic messages.
318
320 None.
321
323 See Shell Command Language . The following additional capabilities are
324 supported on systems supporting the User Portability Utilities option.
325 Command History List
327 When the sh utility is being used interactively, it shall maintain a
328 list of commands previously entered from the terminal in the file named
329 by the HISTFILE environment variable. The type, size, and internal
330 format of this file are unspecified. Multiple sh processes can share
331 access to the file for a user, if file access permissions allow this;
332 see the description of the HISTFILE environment variable.
333 Command Line Editing
335 When sh is being used interactively from a terminal, the current com‐
336 mand and the command history (see fc ) can be edited using vi-mode com‐
337 mand line editing. This mode uses commands, described below, similar to
338 a subset of those described in the vi utility. Implementations may
339 offer other command line editing modes corresponding to other editing
340 utilities.
341 The command set -o vi shall enable vi-mode editing and place sh into vi
343 insert mode (see Command Line Editing (vi-mode) ). This command also
344 shall disable any other editing mode that the implementation may pro‐
345 vide. The command set +o vi disables vi-mode editing.
346 Certain block-mode terminals may be unable to support shell command
348 line editing. If a terminal is unable to provide either edit mode, it
349 need not be possible to set -o vi when using the shell on this termi‐
350 nal.
351 In the following sections, the characters erase, interrupt, kill, and
353 end-of-file are those set by the stty utility.
354 Command Line Editing (vi-mode)
356 In vi editing mode, there shall be a distinguished line, the edit line.
357 All the editing operations which modify a line affect the edit line.
358 The edit line is always the newest line in the command history buffer.
359 With vi-mode enabled, sh can be switched between insert mode and com‐
361 mand mode.
362 When in insert mode, an entered character shall be inserted into the
364 command line, except as noted in vi Line Editing Insert Mode . Upon
365 entering sh and after termination of the previous command, sh shall be
366 in insert mode.
367 Typing an escape character shall switch sh into command mode (see vi
369 Line Editing Command Mode ). In command mode, an entered character
370 shall either invoke a defined operation, be used as part of a multi-
371 character operation, or be treated as an error. A character that is not
372 recognized as part of an editing command shall terminate any specific
373 editing command and shall alert the terminal. Typing the interrupt
374 character in command mode shall cause sh to terminate command line
375 editing on the current command line, reissue the prompt on the next
376 line of the terminal, and reset the command history (see fc ) so that
377 the most recently executed command is the previous command (that is,
378 the command that was being edited when it was interrupted is not reen‐
379 tered into the history).
380 In the following sections, the phrase "move the cursor to the beginning
382 of the word" shall mean "move the cursor to the first character of the
383 current word" and the phrase "move the cursor to the end of the word"
384 shall mean "move the cursor to the last character of the current word".
385 The phrase "beginning of the command line" indicates the point between
386 the end of the prompt string issued by the shell (or the beginning of
387 the terminal line, if there is no prompt string) and the first charac‐
388 ter of the command text.
389 vi Line Editing Insert Mode
391 While in insert mode, any character typed shall be inserted in the cur‐
392 rent command line, unless it is from the following set.
393 <newline>
395 Execute the current command line. If the current command line is
396 not empty, this line shall be entered into the command history
397 (see fc ).
398 erase Delete the character previous to the current cursor position and
400 move the current cursor position back one character. In insert
401 mode, characters shall be erased from both the screen and the
402 buffer when backspacing.
403 interrupt
405 Terminate command line editing with the same effects as
406 described for interrupting command mode; see Command Line Edit‐
407 ing (vi-mode) .
408 kill Clear all the characters from the input line.
410 <control>-V
412 Insert the next character input, even if the character is other‐
413 wise a special insert mode character.
414 <control>-W
416 Delete the characters from the one preceding the cursor to the
417 preceding word boundary. The word boundary in this case is the
418 closer to the cursor of either the beginning of the line or a
419 character that is in neither the blank nor punct character clas‐
420 sification of the current locale.
421 end-of-file
423 Interpreted as the end of input in sh. This interpretation shall
424 occur only at the beginning of an input line. If end-of-file is
425 entered other than at the beginning of the line, the results are
426 unspecified.
427 <ESC> Place sh into command mode.
429 vi Line Editing Command Mode
432 In command mode for the command line editing feature, decimal digits
433 not beginning with 0 that precede a command letter shall be remembered.
434 Some commands use these decimal digits as a count number that affects
435 the operation.
436 The term motion command represents one of the commands:
438 <space> 0 b F l W ^ $ ; E f T w | , B e h t
441 If the current line is not the edit line, any command that modifies the
443 current line shall cause the content of the current line to replace the
444 content of the edit line, and the current line shall become the edit
445 line. This replacement cannot be undone (see the u and U commands
446 below). The modification requested shall then be performed to the edit
447 line. When the current line is the edit line, the modification shall be
448 done directly to the edit line.
449 Any command that is preceded by count shall take a count (the numeric
451 value of any preceding decimal digits). Unless otherwise noted, this
452 count shall cause the specified operation to repeat by the number of
453 times specified by the count. Also unless otherwise noted, a count that
454 is out of range is considered an error condition and shall alert the
455 terminal, but neither the cursor position, nor the command line, shall
456 change.
457 The terms word and bigword are used as defined in the vi description.
459 The term save buffer corresponds to the term unnamed buffer in vi.
460 The following commands shall be recognized in command mode:
462 <newline>
464 Execute the current command line. If the current command line is
465 not empty, this line shall be entered into the command history
466 (see fc ).
467 <control>-L
469 Redraw the current command line. Position the cursor at the same
470 location on the redrawn line.
471 # Insert the character '#' at the beginning of the current command
473 line and treat the resulting edit line as a comment. This line
474 shall be entered into the command history; see fc .
475 = Display the possible shell word expansions (see Word Expansions
477 ) of the bigword at the current command line position.
478 Note:
480 This does not modify the content of the current line, and there‐
481 fore does not cause the current line to become the edit line.
482 These expansions shall be displayed on subsequent terminal lines. If
485 the bigword contains none of the characters '?', '*', or '[', an aster‐
486 isk ( '*' ) shall be implicitly assumed at the end. If any directories
487 are matched, these expansions shall have a '/' character appended.
488 After the expansion, the line shall be redrawn, the cursor repositioned
489 at the current cursor position, and sh shall be placed in command mode.
490 \ Perform pathname expansion (see Pathname Expansion ) on the cur‐
492 rent bigword, up to the largest set of characters that can be
493 matched uniquely. If the bigword contains none of the charac‐
494 ters '?', '*', or '[', an asterisk ( '*' ) shall be implicitly
495 assumed at the end. This maximal expansion then shall replace
496 the original bigword in the command line, and the cursor shall
497 be placed after this expansion. If the resulting bigword com‐
498 pletely and uniquely matches a directory, a '/' character shall
499 be inserted directly after the bigword. If some other file is
500 completely matched, a single <space> shall be inserted after the
501 bigword. After this operation, sh shall be placed in insert
502 mode.
503 * Perform pathname expansion on the current bigword and insert all
505 expansions into the command to replace the current bigword, with
506 each expansion separated by a single <space>. If at the end of
507 the line, the current cursor position shall be moved to the
508 first column position following the expansions and sh shall be
509 placed in insert mode. Otherwise, the current cursor position
510 shall be the last column position of the first character after
511 the expansions and sh shall be placed in insert mode. If the
512 current bigword contains none of the characters '?', '*', or
513 '[', before the operation, an asterisk shall be implicitly
514 assumed at the end.
515 @letter
517 Insert the value of the alias named _letter. The symbol letter
518 represents a single alphabetic character from the portable char‐
519 acter set; implementations may support additional characters as
520 an extension. If the alias _letter contains other editing com‐
521 mands, these commands shall be performed as part of the inser‐
522 tion. If no alias _letter is enabled, this command shall have no
523 effect.
524 [count]~
526 Convert, if the current character is a lowercase letter, to the
527 equivalent uppercase letter and vice versa, as prescribed by the
528 current locale. The current cursor position then shall be
529 advanced by one character. If the cursor was positioned on the
530 last character of the line, the case conversion shall occur, but
531 the cursor shall not advance. If the '~' command is preceded by
532 a count, that number of characters shall be converted, and the
533 cursor shall be advanced to the character position after the
534 last character converted. If the count is larger than the number
535 of characters after the cursor, this shall not be considered an
536 error; the cursor shall advance to the last character on the
537 line.
538 [count].
540 Repeat the most recent non-motion command, even if it was exe‐
541 cuted on an earlier command line. If the previous command was
542 preceded by a count, and no count is given on the '.' command,
543 the count from the previous command shall be included as part of
544 the repeated command. If the '.' command is preceded by a count,
545 this shall override any count argument to the previous command.
546 The count specified in the '.' command shall become the count
547 for subsequent '.' commands issued without a count.
548 [number]v
550 Invoke the vi editor to edit the current command line in a tem‐
551 porary file. When the editor exits, the commands in the tempo‐
552 rary file shall be executed and placed in the command history.
553 If a number is included, it specifies the command number in the
554 command history to be edited, rather than the current command
555 line.
556 [count]l (ell)
558 [count]<space>
560 Move the current cursor position to the next character position.
562 If the cursor was positioned on the last character of the line,
563 the terminal shall be alerted and the cursor shall not be
564 advanced. If the count is larger than the number of characters
565 after the cursor, this shall not be considered an error; the
566 cursor shall advance to the last character on the line.
567 [count]h
569 Move the current cursor position to the countth (default 1) pre‐
570 vious character position. If the cursor was positioned on the
571 first character of the line, the terminal shall be alerted and
572 the cursor shall not be moved. If the count is larger than the
573 number of characters before the cursor, this shall not be con‐
574 sidered an error; the cursor shall move to the first character
575 on the line.
576 [count]w
578 Move to the start of the next word. If the cursor was positioned
579 on the last character of the line, the terminal shall be alerted
580 and the cursor shall not be advanced. If the count is larger
581 than the number of words after the cursor, this shall not be
582 considered an error; the cursor shall advance to the last char‐
583 acter on the line.
584 [count]W
586 Move to the start of the next bigword. If the cursor was posi‐
587 tioned on the last character of the line, the terminal shall be
588 alerted and the cursor shall not be advanced. If the count is
589 larger than the number of bigwords after the cursor, this shall
590 not be considered an error; the cursor shall advance to the last
591 character on the line.
592 [count]e
594 Move to the end of the current word. If at the end of a word,
595 move to the end of the next word. If the cursor was positioned
596 on the last character of the line, the terminal shall be alerted
597 and the cursor shall not be advanced. If the count is larger
598 than the number of words after the cursor, this shall not be
599 considered an error; the cursor shall advance to the last char‐
600 acter on the line.
601 [count]E
603 Move to the end of the current bigword. If at the end of a big‐
604 word, move to the end of the next bigword. If the cursor was
605 positioned on the last character of the line, the terminal shall
606 be alerted and the cursor shall not be advanced. If the count is
607 larger than the number of bigwords after the cursor, this shall
608 not be considered an error; the cursor shall advance to the last
609 character on the line.
610 [count]b
612 Move to the beginning of the current word. If at the beginning
613 of a word, move to the beginning of the previous word. If the
614 cursor was positioned on the first character of the line, the
615 terminal shall be alerted and the cursor shall not be moved. If
616 the count is larger than the number of words preceding the cur‐
617 sor, this shall not be considered an error; the cursor shall
618 return to the first character on the line.
619 [count]B
621 Move to the beginning of the current bigword. If at the begin‐
622 ning of a bigword, move to the beginning of the previous big‐
623 word. If the cursor was positioned on the first character of
624 the line, the terminal shall be alerted and the cursor shall not
625 be moved. If the count is larger than the number of bigwords
626 preceding the cursor, this shall not be considered an error; the
627 cursor shall return to the first character on the line.
628 ^ Move the current cursor position to the first character on the
630 input line that is not a <blank>.
631 $ Move to the last character position on the current command line.
633 0 (Zero.) Move to the first character position on the current com‐
635 mand line.
636 [count]|
638 Move to the countth character position on the current command
639 line. If no number is specified, move to the first position. The
640 first character position shall be numbered 1. If the count is
641 larger than the number of characters on the line, this shall not
642 be considered an error; the cursor shall be placed on the last
643 character on the line.
644 [count]fc
646 Move to the first occurrence of the character 'c' that occurs
647 after the current cursor position. If the cursor was positioned
648 on the last character of the line, the terminal shall be alerted
649 and the cursor shall not be advanced. If the character 'c' does
650 not occur in the line after the current cursor position, the
651 terminal shall be alerted and the cursor shall not be moved.
652 [count]Fc
654 Move to the first occurrence of the character 'c' that occurs
655 before the current cursor position. If the cursor was positioned
656 on the first character of the line, the terminal shall be
657 alerted and the cursor shall not be moved. If the character 'c'
658 does not occur in the line before the current cursor position,
659 the terminal shall be alerted and the cursor shall not be moved.
660 [count]tc
662 Move to the character before the first occurrence of the charac‐
663 ter 'c' that occurs after the current cursor position. If the
664 cursor was positioned on the last character of the line, the
665 terminal shall be alerted and the cursor shall not be advanced.
666 If the character 'c' does not occur in the line after the cur‐
667 rent cursor position, the terminal shall be alerted and the cur‐
668 sor shall not be moved.
669 [count]Tc
671 Move to the character after the first occurrence of the charac‐
672 ter 'c' that occurs before the current cursor position. If the
673 cursor was positioned on the first character of the line, the
674 terminal shall be alerted and the cursor shall not be moved. If
675 the character 'c' does not occur in the line before the current
676 cursor position, the terminal shall be alerted and the cursor
677 shall not be moved.
678 [count];
680 Repeat the most recent f, F, t, or T command. Any number argu‐
681 ment on that previous command shall be ignored. Errors are those
682 described for the repeated command.
683 [count],
685 Repeat the most recent f, F, t, or T command. Any number argu‐
686 ment on that previous command shall be ignored. However, reverse
687 the direction of that command.
688 a Enter insert mode after the current cursor position. Characters
690 that are entered shall be inserted before the next character.
691 A Enter insert mode after the end of the current command line.
693 i Enter insert mode at the current cursor position. Characters
695 that are entered shall be inserted before the current character.
696 I Enter insert mode at the beginning of the current command line.
698 R Enter insert mode, replacing characters from the command line
700 beginning at the current cursor position.
701 [count]cmotion
703 Delete the characters between the current cursor position and
705 the cursor position that would result from the specified motion
706 command. Then enter insert mode before the first character fol‐
707 lowing any deleted characters. If count is specified, it shall
708 be applied to the motion command. A count shall be ignored for
709 the following motion commands:
710 0 ^ $ c
713 If the motion command is the character 'c', the current command line
715 shall be cleared and insert mode shall be entered. If the motion com‐
716 mand would move the current cursor position toward the beginning of the
717 command line, the character under the current cursor position shall not
718 be deleted. If the motion command would move the current cursor posi‐
719 tion toward the end of the command line, the character under the cur‐
720 rent cursor position shall be deleted. If the count is larger than the
721 number of characters between the current cursor position and the end of
722 the command line toward which the motion command would move the cursor,
723 this shall not be considered an error; all of the remaining characters
724 in the aforementioned range shall be deleted and insert mode shall be
725 entered. If the motion command is invalid, the terminal shall be
726 alerted, the cursor shall not be moved, and no text shall be deleted.
727 C Delete from the current character to the end of the line and
729 enter insert mode at the new end-of-line.
730 S Clear the entire edit line and enter insert mode.
732 [count]rc
734 Replace the current character with the character 'c' . With a
735 number count, replace the current and the following count-1
736 characters. After this command, the current cursor position
737 shall be on the last character that was changed. If the count is
738 larger than the number of characters after the cursor, this
739 shall not be considered an error; all of the remaining charac‐
740 ters shall be changed.
741 [count]_
743 Append a <space> after the current character position and then
744 append the last bigword in the previous input line after the
745 <space>. Then enter insert mode after the last character just
746 appended. With a number count, append the countth bigword in the
747 previous line.
748 [count]x
750 Delete the character at the current cursor position and place
751 the deleted characters in the save buffer. If the cursor was
752 positioned on the last character of the line, the character
753 shall be deleted and the cursor position shall be moved to the
754 previous character (the new last character). If the count is
755 larger than the number of characters after the cursor, this
756 shall not be considered an error; all the characters from the
757 cursor to the end of the line shall be deleted.
758 [count]X
760 Delete the character before the current cursor position and
761 place the deleted characters in the save buffer. The character
762 under the current cursor position shall not change. If the cur‐
763 sor was positioned on the first character of the line, the ter‐
764 minal shall be alerted, and the X command shall have no effect.
765 If the line contained a single character, the X command shall
766 have no effect. If the line contained no characters, the termi‐
767 nal shall be alerted and the cursor shall not be moved. If the
768 count is larger than the number of characters before the cursor,
769 this shall not be considered an error; all the characters from
770 before the cursor to the beginning of the line shall be deleted.
771 [count]dmotion
773 Delete the characters between the current cursor position and
775 the character position that would result from the motion com‐
776 mand. A number count repeats the motion command count times. If
777 the motion command would move toward the beginning of the com‐
778 mand line, the character under the current cursor position shall
779 not be deleted. If the motion command is d, the entire current
780 command line shall be cleared. If the count is larger than the
781 number of characters between the current cursor position and the
782 end of the command line toward which the motion command would
783 move the cursor, this shall not be considered an error; all of
784 the remaining characters in the aforementioned range shall be
785 deleted. The deleted characters shall be placed in the save buf‐
786 fer.
787 D Delete all characters from the current cursor position to the
789 end of the line. The deleted characters shall be placed in the
790 save buffer.
791 [count]ymotion
793 Yank (that is, copy) the characters from the current cursor
795 position to the position resulting from the motion command into
796 the save buffer. A number count shall be applied to the motion
797 command. If the motion command would move toward the beginning
798 of the command line, the character under the current cursor
799 position shall not be included in the set of yanked characters.
800 If the motion command is y, the entire current command line
801 shall be yanked into the save buffer. The current cursor posi‐
802 tion shall be unchanged. If the count is larger than the number
803 of characters between the current cursor position and the end of
804 the command line toward which the motion command would move the
805 cursor, this shall not be considered an error; all of the
806 remaining characters in the aforementioned range shall be
807 yanked.
808 Y Yank the characters from the current cursor position to the end
810 of the line into the save buffer. The current character position
811 shall be unchanged.
812 [count]p
814 Put a copy of the current contents of the save buffer after the
815 current cursor position. The current cursor position shall be
816 advanced to the last character put from the save buffer. A count
817 shall indicate how many copies of the save buffer shall be put.
818 [count]P
820 Put a copy of the current contents of the save buffer before the
821 current cursor position. The current cursor position shall be
822 moved to the last character put from the save buffer. A count
823 shall indicate how many copies of the save buffer shall be put.
824 u Undo the last command that changed the edit line. This operation
826 shall not undo the copy of any command line to the edit line.
827 U Undo all changes made to the edit line. This operation shall not
829 undo the copy of any command line to the edit line.
830 [count]k
832 [count]-
834 Set the current command line to be the countth previous command
835 line in the shell command history. If count is not specified, it
836 shall default to 1. The cursor shall be positioned on the first
837 character of the new command. If a k or - command would retreat
838 past the maximum number of commands in effect for this shell
839 (affected by the HISTSIZE environment variable), the terminal
840 shall be alerted, and the command shall have no effect.
841 [count]j
843 [count]+
845 Set the current command line to be the countth next command line
846 in the shell command history. If count is not specified, it
847 shall default to 1. The cursor shall be positioned on the first
848 character of the new command. If a j or + command advances past
849 the edit line, the current command line shall be restored to the
850 edit line and the terminal shall be alerted.
851 [number]G
853 Set the current command line to be the oldest command line
854 stored in the shell command history. With a number number, set
855 the current command line to be the command line number in the
856 history. If command line number does not exist, the terminal
857 shall be alerted and the command line shall not be changed.
858 /pattern<newline>
860 Move backwards through the command history, searching for the
862 specified pattern, beginning with the previous command line.
863 Patterns use the pattern matching notation described in Pattern
864 Matching Notation, except that the '^' character shall have spe‐
865 cial meaning when it appears as the first character of pattern.
866 In this case, the '^' is discarded and the characters after the
867 '^' shall be matched only at the beginning of a line. Commands
868 in the command history shall be treated as strings, not as file‐
869 names. If the pattern is not found, the current command line
870 shall be unchanged and the terminal is alerted. If it is found
871 in a previous line, the current command line shall be set to
872 that line and the cursor shall be set to the first character of
873 the new command line.
874 If pattern is empty, the last non-empty pattern provided to / or ?
876 shall be used. If there is no previous non-empty pattern, the terminal
877 shall be alerted and the current command line shall remain unchanged.
878 ?pattern<newline>
880 Move forwards through the command history, searching for the
882 specified pattern, beginning with the next command line. Pat‐
883 terns use the pattern matching notation described in Pattern
884 Matching Notation, except that the '^' character shall have spe‐
885 cial meaning when it appears as the first character of pattern.
886 In this case, the '^' is discarded and the characters after the
887 '^' shall be matched only at the beginning of a line. Commands
888 in the command history shall be treated as strings, not as file‐
889 names. If the pattern is not found, the current command line
890 shall be unchanged and the terminal alerted. If it is found in a
891 following line, the current command line shall be set to that
892 line and the cursor shall be set to the fist character of the
893 new command line.
894 If pattern is empty, the last non-empty pattern provided to / or ?
896 shall be used. If there is no previous non-empty pattern, the terminal
897 shall be alerted and the current command line shall remain unchanged.
898 n Repeat the most recent / or ? command. If there is no previous /
900 or ?, the terminal shall be alerted and the current command line
901 shall remain unchanged.
902 N Repeat the most recent / or ? command, reversing the direction
904 of the search. If there is no previous / or ?, the terminal
905 shall be alerted and the current command line shall remain
906 unchanged.
907
910 The following exit values shall be returned:
911 0 The script to be executed consisted solely of zero or more blank
913 lines or comments, or both.
914 1-125 A non-interactive shell detected a syntax, redirection, or vari‐
916 able assignment error.
917 127 A specified command_file could not be found by a non-interactive
919 shell.
920 Otherwise, the shell shall return the exit status of the last command
923 it invoked or attempted to invoke (see also the exit utility in Special
924 Built-In Utilities ).
925
927 See Consequences of Shell Errors .
928 The following sections are informative.
930
932 Standard input and standard error are the files that determine whether
933 a shell is interactive when -i is not specified. For example:
934 sh > file
937 and:
939 sh 2> file
942 create interactive and non-interactive shells, respectively. Although
944 both accept terminal input, the results of error conditions are differ‐
945 ent, as described in Consequences of Shell Errors ; in the second exam‐
946 ple a redirection error encountered by a special built-in utility
947 aborts the shell.
948 A conforming application must protect its first operand, if it starts
950 with a plus sign, by preceding it with the "--" argument that denotes
951 the end of the options.
952 Applications should note that the standard PATH to the shell cannot be
954 assumed to be either /bin/sh or /usr/bin/sh, and should be determined
955 by interrogation of the PATH returned by getconf PATH, ensuring that
956 the returned pathname is an absolute pathname and not a shell built-in.
957 For example, to determine the location of the standard sh utility:
959 command -v sh
962 On some implementations this might return:
964 /usr/xpg4/bin/sh
967 Furthermore, on systems that support executable scripts (the "#!" con‐
969 struct), it is recommended that applications using executable scripts
970 install them using getconf -v to determine the shell pathname and
971 update the "#!" script appropriately as it is being installed (for
972 example, with sed). For example:
973 #
976 # Installation time script to install correct POSIX shell pathname
977 #
978 # Get list of paths to check
979 #
980 Sifs=$IFS
981 IFS=:
982 set $(getconf PATH)
983 IFS=$Sifs
984 #
985 # Check each path for 'sh'
986 #
987 for i in $@
988 do
989 if [ -f ${i}/sh ];
990 then
991 Pshell=${i}/sh
992 fi
993 done
994 #
995 # This is the list of scripts to update. They should be of the
996 # form '${name}.source' and will be transformed to '${name}'.
997 # Each script should begin:
998 #
999 # !INSTALLSHELLPATH -p
1000 #
1001 scripts="a b c"
1002 #
1003 # Transform each script
1004 #
1005 for i in ${scripts}
1006 do
1007 sed -e "s|INSTALLSHELLPATH|${Pshell}|" < ${i}.source > ${i}
1008 done
1009
1011 1. Execute a shell command from a string:
1012 sh -c "cat myfile"
1015 2. Execute a shell script from a file in the current directory:
1017 sh my_shell_cmds
1020
1022 The sh utility and the set special built-in utility share a common set
1023 of options.
1024 The KornShell ignores the contents of IFS upon entry to the script. A
1026 conforming application cannot rely on importing IFS. One justification
1027 for this, beyond security considerations, is to assist possible future
1028 shell compilers. Allowing IFS to be imported from the environment pre‐
1029 vents many optimizations that might otherwise be performed via dataflow
1030 analysis of the script itself.
1031 The text in the STDIN section about non-blocking reads concerns an
1033 instance of sh that has been invoked, probably by a C-language program,
1034 with standard input that has been opened using the O_NONBLOCK flag; see
1035 open() in the System Interfaces volume of IEEE Std 1003.1-2001. If the
1036 shell did not reset this flag, it would immediately terminate because
1037 no input data would be available yet and that would be considered the
1038 same as end-of-file.
1039 The options associated with a restricted shell (command name rsh and
1041 the -r option) were excluded because the standard developers considered
1042 that the implied level of security could not be achieved and they did
1043 not want to raise false expectations.
1044 On systems that support set-user-ID scripts, a historical trapdoor has
1046 been to link a script to the name -i. When it is called by a sequence
1047 such as:
1048 sh -
1051 or by:
1053 #! usr/bin/sh -
1056 the historical systems have assumed that no option letters follow.
1058 Thus, this volume of IEEE Std 1003.1-2001 allows the single hyphen to
1059 mark the end of the options, in addition to the use of the regular "--"
1060 argument, because it was considered that the older practice was so per‐
1061 vasive. An alternative approach is taken by the KornShell, where real
1062 and effective user/group IDs must match for an interactive shell; this
1063 behavior is specifically allowed by this volume of
1064 IEEE Std 1003.1-2001.
1065 Note: There are other problems with set-user-ID scripts that the two
1067 approaches described here do not resolve.
1068 The initialization process for the history file can be dependent on the
1071 system start-up files, in that they may contain commands that effec‐
1072 tively preempt the user's settings of HISTFILE and HISTSIZE. For exam‐
1073 ple, function definition commands are recorded in the history file,
1074 unless the set -o nolog option is set. If the system administrator
1075 includes function definitions in some system start-up file called
1076 before the ENV file, the history file is initialized before the user
1077 gets a chance to influence its characteristics. In some historical
1078 shells, the history file is initialized just after the ENV file has
1079 been processed. Therefore, it is implementation-defined whether
1080 changes made to HISTFILE after the history file has been initialized
1081 are effective.
1082 The default messages for the various MAIL -related messages are unspec‐
1084 ified because they vary across implementations. Typical messages are:
1085 "you have mail\n"
1088 or:
1090 "you have new mail\n"
1093 It is important that the descriptions of command line editing refer to
1095 the same shell as that in IEEE Std 1003.1-2001 so that interactive
1096 users can also be application programmers without having to deal with
1097 programmatic differences in their two environments. It is also essen‐
1098 tial that the utility name sh be specified because this explicit util‐
1099 ity name is too firmly rooted in historical practice of application
1100 programs for it to change.
1101 Consideration was given to mandating a diagnostic message when attempt‐
1103 ing to set vi-mode on terminals that do not support command line edit‐
1104 ing. However, it is not historical practice for the shell to be cog‐
1105 nizant of all terminal types and thus be able to detect inappropriate
1106 terminals in all cases. Implementations are encouraged to supply diag‐
1107 nostics in this case whenever possible, rather than leaving the user in
1108 a state where editing commands work incorrectly.
1109 In early proposals, the KornShell-derived emacs mode of command line
1111 editing was included, even though the emacs editor itself was not. The
1112 community of emacs proponents was adamant that the full emacs editor
1113 not be standardized because they were concerned that an attempt to
1114 standardize this very powerful environment would encourage vendors to
1115 ship strictly conforming versions lacking the extensibility required by
1116 the community. The author of the original emacs program also expressed
1117 his desire to omit the program. Furthermore, there were a number of
1118 historical systems that did not include emacs, or included it without
1119 supporting it, but there were very few that did not include and support
1120 vi. The shell emacs command line editing mode was finally omitted
1121 because it became apparent that the KornShell version and the editor
1122 being distributed with the GNU system had diverged in some respects.
1123 The author of emacs requested that the POSIX emacs mode either be
1124 deleted or have a significant number of unspecified conditions.
1125 Although the KornShell author agreed to consider changes to bring the
1126 shell into alignment, the standard developers decided to defer specifi‐
1127 cation at that time. At the time, it was assumed that convergence on an
1128 acceptable definition would occur for a subsequent draft, but that has
1129 not happened, and there appears to be no impetus to do so. In any case,
1130 implementations are free to offer additional command line editing modes
1131 based on the exact models of editors their users are most comfortable
1132 with.
1133 Early proposals had the following list entry in vi Line Editing Insert
1135 Mode :
1136 \ If followed by the erase or kill character, that character shall
1138 be inserted into the input line. Otherwise, the backslash itself
1139 shall be inserted into the input line.
1140 However, this is not actually a feature of sh command line editing
1143 insert mode, but one of some historical terminal line drivers. Some
1144 conforming implementations continue to do this when the stty iexten
1145 flag is set.
1146
1148 None.
1149
1151 Shell Command Language, cd, echo, exit(), fc, pwd, read(), set, stty,
1152 test, umask(), vi, the System Interfaces volume of
1153 IEEE Std 1003.1-2001, dup(), exec, exit(), fork(), open(), pipe(), sig‐
1154 nal(), system(), ulimit(), umask(), wait()
1155
1157 Portions of this text are reprinted and reproduced in electronic form
1158 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
1159 -- Portable Operating System Interface (POSIX), The Open Group Base
1160 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
1161 Electrical and Electronics Engineers, Inc and The Open Group. In the
1162 event of any discrepancy between this version and the original IEEE and
1163 The Open Group Standard, the original IEEE and The Open Group Standard
1164 is the referee document. The original Standard can be obtained online
1165 at http://www.opengroup.org/unix/online.html .
1166IEEE/The Open Group 2003 SH(1P)