1PERLDL(1)             User Contributed Perl Documentation            PERLDL(1)
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NAME

6       perldl - Simple shell for PDL (see also pdl2)
7

SYNOPSIS

9       Use PDL interactively:
10
11         bash$ perldl
12         pdl> $x = sequence(10) # or any other perl or PDL command
13
14         bash$ pdl
15         pdl> print "Hello, world!\n";
16
17       Run a script:
18
19         bash$ cat > pdlscript
20         #!/usr/bin/pdl
21         print "Hello, world!\n";
22         ...
23

DESCRIPTION

25       The program perldl is a simple shell (written in perl) for interactive
26       use of PDL.  It consists of a command-line interface that supports
27       immediate interpretation of perl commands and expressions.  Perl
28       expressions, including PDL constructs, can be entered directly at the
29       keyboard and are compiled and executed immediately.  The syntax is not
30       exactly identical to Perl, in that under most circumstances ending a
31       line causes immediate execution of the command entered so far (no
32       trailing ';' is required).
33
34       The synonym pdl is a compiled executable that is useful as a script
35       interpreter using UNIX shebang ("#!") syntax.  This is useful for
36       generating and re-executing command-journal files from perldl.
37
38       The perldl shell runs an initial startup file ("~/.perldlrc") that can
39       be used to pre-load perl modules or configure the global perl
40       environment.  It features a path mechanism for autoloading perl
41       subroutines.  There is a command-history mechanism, and several other
42       useful features such as command preprocessing, shortcuts for commonly
43       used commands such as "print", and the ability to execute arbitrary
44       code whenever a prompt is printed.
45
46       Depending on your configuration settings, perldl can be set to honor or
47       ignore the ^D (end-of-file) character when sent from a terminal, or to
48       attempt to do the Right Thing when a block construct spanning multiple
49       lines is encountered.
50
51       perldl and pdl support several command-line options, which are
52       discussed near the end of this document.
53
54   Reference manual & online help
55       The PDL reference manual and online help are available from within
56       perldl, using the help and apropos commands (which may also be
57       abbreviated ? and ??.)   The help command alone prints a summary of
58       help syntax, and help <module-name> will print POD documentation from
59       the module you mention (POD is the Perl format for embedding
60       documentation in your perl code; see perlpod for details).
61
62       If you include POD documentation in your autoload subroutines (see path
63       mechanism below), then both help and apropos will find it and be able
64       to format and display it on demand.
65
66   History mechanism
67       If you have the perl modules ReadLines and ReadKeys installed, then
68       perldl supports a history and line-editing mechanism using editing keys
69       similar to "emacs". The last 500 commands are always stored in the file
70       .perldl_hist in your home directory between sessions.  Set
71       $PERLDL::HISTFILESIZE to change the number of lines saved.  The command
72       "l [number]" shows you the last "number" commands you typed where
73       "number" defaults to 20.
74
75       e.g.:
76
77          bash$ perldl
78          ReadLines enabled
79          pdl> $x = rfits "foo.fits"
80          BITPIX =  -32  size = 88504 pixels
81          Reading  354016 bytes
82          BSCALE =  &&  BZERO =
83
84          pdl> imag log($x+400)
85          Displaying 299 x 296 image from 4.6939525604248 to 9.67116928100586 ...
86
87   Command execution
88       If you enter a simple command at the perldl command line, it is
89       immediately executed in a Perl "eval()".  The environment is almost
90       identical to that within a perl script, with some important exceptions:
91
92       •  $_ is not preserved across lines
93
94          $_ is used to hold the command line for initial processing, so at
95          the beginning of processing of each command line, $_ contains the
96          command itself.  Use variables other than $_ to store values across
97          lines.
98
99       •  Scope is not preserved across lines
100
101          Each command line is executed in a separate "eval" block within
102          perl, so scoping commands such as "my" and "local" may not perform
103          exactly as expected -- in particular, if you declare a variable with
104          "my", it is local to the particular command line on which you typed
105          the "my" command, which means that it will evaporate before the next
106          prompt is printed.  (You can use "my" variables in a multi-line
107          block or to isolate values within a single command line, of course).
108
109            NOTE: pdl2 preserves lexical scope between lines.
110
111       •  Execution is immediate
112
113          Under most circumstances, as soon as you end a line of input the
114          line is parsed and executed.  This breaks Perl's normal dependence
115          on semicolons as command delimiters.  For example, the two-line
116          expression
117
118            print "Hello ",
119               "world";
120
121          prints the phrase "Hello world" in Perl, but (under most
122          circumstances) "Hello " in perldl.
123
124       •  Multi-line execution
125
126          In multiline mode (which is enabled by default, see Shell variables,
127          below), perldl searches for searches for block-like constructs with
128          curly braces, parentheses, quotes, and related delimiters.  If you
129          leave such a construct open, perldl accepts more lines of input
130          until you close the construct or explicitly end the multi-line
131          expression with ^D.   Following the example above, the phrase
132
133            { print "Hello ",
134                 "world"; }
135
136          will print "Hello world" from either Perl or (in multi-line mode)
137          perldl.
138
139          Warning: The multi-line parsing uses Damian Conway's Text::Balanced
140          module, which contains some flaws -- so it can be fooled by quote-
141          like operators such as "q/.../", included POD documentation, multi-
142          line "<<" quotes, and some particularly bizarre-but-valid "m/.../"
143          matches and "s/.../.../" substitutions.  In such cases, use ^D to
144          close out the multi-line construct and force compilation-and-
145          execution.
146
147       If you want to preserve this behavior in a script (for example to
148       replay a command journal file; see below on how to create one), you can
149       use pdl instead of perl as the interpreter in the script's initial
150       shebang line.
151
152   Terminating "perldl"
153       A "perldl" session can be terminated with any of the commands "quit",
154       "exit" or the shorthands "x" or "q".  If EOF handling is switched on
155       (the default) you can also type ^D at the command prompt.
156
157       If the command input is NOT a terminal (for example if you are running
158       from a command journal file), then EOF will always terminate perldl.
159
160   Terminating commands (Ctrl-C handling)
161       Commands executed within "perldl" can be terminated prematurely using
162       "Ctrl-C" (or whichever key sequence sends an INT signal to the process
163       on your terminal). Provided your PDL code does not ignore "sigint"s
164       this should throw you back at the "perldl" command prompt:
165
166         pdl> $result = start_lengthy_computation()
167          <Ctrl-C>
168        Ctrl-C detected
169
170         pdl>
171
172   Shortcuts and aliases
173       •   The shell aliases "p" to be a convenient short form of "print",
174           e.g.
175
176              pdl> p ones 5,3
177
178              [
179               [1 1 1 1 1]
180               [1 1 1 1 1]
181               [1 1 1 1 1]
182              ]
183
184       •   "q" and "x" are short-hand for "quit".
185
186       •   "l" lists the history buffer
187
188             pdl> l # list last 20 commands
189
190             pdl> l 40 # list last 40 commands
191
192       •   "?" is an alias for help
193
194             pdl> ? pdl2    # get help for new pdl2 shell
195
196       •   "??" is an alias for apropos
197
198             pdl> ?? PDL::Doc
199
200       •   help, apropos, usage and sig: all words after these commands are
201           used verbatim and not evaluated by perl. So you can write, e.g.,
202
203             pdl> help help
204
205           instead of
206
207             pdl> help 'help'
208
209   Command-line options
210       perldl and pdl support several command-line options to adjust the
211       behavior of the session.  Most of them are equivalent to commands that
212       can be entered at the pdl> prompt.  They are:
213
214       -glut
215           Load OpenGL when starting the shell (the perl OpenGL module, which
216           is available from CPAN must be installed).  This enables readline
217           event loop processing.  Don't use with -tk.
218
219       -tk Load Tk when starting the shell (the perl Tk module, which is
220           available from CPAN must be installed).  This enables readline
221           event loop processing.  Don't use with -glut.
222
223       -f file
224           Loads the file before processing any user input. Any errors during
225           the execution of the file are fatal.
226
227       -w  Runs with warning messages (i.e. the normal perl "-w" warnings)
228           turned-on.
229
230       -M module
231           Loads the module before processing any user input.  Compare
232           corresponding "perl" switch.
233
234       -m module
235           Unloads the module before processing any user input.
236
237       -I directory
238           Adds directory to the include path. (i.e. the @INC array) Compare
239           corresponding "perl" switch.
240
241       -V  Prints a summary of PDL config. This information should be included
242           with any PDL bug report. Compare corresponding "perl" switch.
243
244   The startup file ~/.perldlrc
245       If the file ~/.perldlrc is found it is sourced at start-up to load
246       default modules, set shell variables, etc. If it is NOT found the
247       distribution file PDL/default.perldlrc is read instead. This loads
248       various modules considered useful by default, and which ensure
249       compatibility with v1.11. If you don't like this and want a more
250       streamlined set of your own favourite modules simple create your own
251       ~/.perldlrc.  You may wish to start from the existing
252       PDL/default.perldlrc as a template since it will not be sourced once
253       you replace it with your own version.
254
255       To set even more local defaults the file  local.perldlrc (in the
256       current directory) is sourced if found. This lets you load modules and
257       define subroutines for the project in the current directory.
258
259       The name is chosen specifically because it was found hidden files were
260       NOT wanted in these circumstances.
261
262       The startup file should normally include "use PDL::AutoLoader;", as
263       many of the nicer interactive features won't work without it.
264
265   Shell variables
266       Shell variables: (Note: if you don't like the defaults change them in
267       ~/.perldlrc)
268
269       •   $PERLDL::ESCAPE  - default value '#'
270
271           Any line starting with this character is treated as a shell escape.
272           The default value is chosen because it escapes the code from the
273           standard perl interpreter.
274
275       •   $PERLDL::HISTFILESIZE  - default value 500
276
277           This is the number of lines of perldl shell command history to
278           keep.
279
280       •   $PERLDL::PAGER - default value "more"
281
282           External program to filter the output of commands.  Using "more"
283           prints output one screenful at a time.  On Unix, setting page(1)
284           and $PERLDL::PAGER to "tee -a outfile" will keep a record of the
285           output generated by subsequent perldl commands (without paging).
286
287       •   $PERLDL::PROMPT - default value 'pdl> '
288
289           Enough said  But can also be set to a subroutine reference, e.g.
290           $PERLDL::PROMPT = sub {join(':',(gmtime)[2,1,0]).'> '} puts the
291           current time into the prompt.
292
293       •   $PERLDL::MULTI - default value 1
294
295           If this is set to a true value, then perldl will parse multi-line
296           perl blocks: your input will not be executed until you finish a
297           line with no outstanding group operators (such as quotes, blocks,
298           parenthesis, or brackets) still active.  Continuation lines have a
299           different prompt that shows you what delimiters are still active.
300
301           Note that this is not (yet!) a complete perl parser.  In
302           particular, Text::Balanced appears to be able to ignore quoting
303           operatores like "q/ ... /" within a line, but not to be able to
304           extend them across lines.  Likewise, there is no support for the
305           '<<' operator.
306
307           Multiline conventional strings and {}, [], and () groupings are
308           well supported.
309
310       •   $PERLDL::NO_EOF - default value 0 / 1 on MSWin32
311
312           Protects against accidental use of "^D" from the terminal.  If this
313           is set to a true value, then you can't accidentally exit perldl by
314           typing "^D".  If you set it to a value larger than 1 (and
315           PERLDL::MULTI is set), then you can't use "^D" to exit multiline
316           commands either.  If you're piping commands in from a file or pipe,
317           this variable has no effect.
318
319       •   $HOME
320
321           The user's home directory
322
323       •   $PERLDL::TERM
324
325           This is the Term::ReadLine object associated with the perldl shell.
326           It can be used by routines called from perldl if your command is
327           interactive.
328
329       •   $PDL::toolongtoprint
330
331           The maximal size pdls to print (defaults to 10,000 elements).  This
332           is not just a "perldl" or "pdl2" variable but it is something that
333           is usually needed in an interactive debugging session.
334
335   Executing scripts from the "perldl" prompt
336       A useful idiom for developing perldl scripts or editing functions on-
337       line is
338
339         pdl> # emacs script &
340           -- add perldl code to script and save the file
341
342         pdl> do 'script'
343
344       -- substitute your favourite window-based editor for 'emacs' (you may
345       also need to change the '&' on non-Unix systems).
346
347       Running "do 'script'" again updates any variables and function
348       definitions from the current version of 'script'.
349
350   Executing perldl scripts from the command line
351       PDL scripts are just perl scripts that happen to use PDL (and possibly
352       PDL::NiceSlice).  But for the truly lazy, perldl can be invokes as a
353       script interpreter.  Because perldl is itself an interpreted perl
354       script, most unices won't allow you to say "#!/usr/bin/perldl" at the
355       top of your script.
356
357       Instead, say "#!/usr/bin/pdl" and your script will be executed exactly
358       as if you typed it, line-by-line, into the perldl shell.
359
360   Command preprocessing
361       NOTE: This feature is used by default by PDL::NiceSlice.  See below for
362       more about slicing at the "perldl" prompt
363
364       In some cases, it is convenient to process commands before they are
365       sent to perl for execution. For example, this is the case where the
366       shell is being presented to people unfamiliar with perl but who wish to
367       take advantage of commands added locally (eg by automatically quoting
368       arguments to certain commands).
369
370       *NOTE*: The preprocessing interface has changed from earlier versions!
371       The old way using $PERLDL::PREPROCESS will still work but is strongly
372       deprecated and might go away in the future.
373
374       You can enable preprocessing by registering a filter with the
375       "preproc_add" function. "preproc_add" takes one argument which is the
376       filter to be installed. A filter is a Perl code reference (usually set
377       in a local configuration file) that will be called, with the current
378       command string as argument, just prior to the string being executed by
379       the shell. The modified string should be returned. Note that you can
380       make "perldl" completely unusable if you fail to return the modified
381       string; quitting is then your only option.
382
383       Filters can be removed from the preprocessing pipeline by calling
384       "preproc_del" with the filter to be removed as argument.  To find out
385       if a filter is currently installed in the preprocessing pipeline use
386       "preproc_registered":
387
388         pdl> preproc_add $myfilter unless preproc_registered $myfilter;
389
390       Previous versions of "perldl" used the variable $PERLDL::PREPROCESS.
391       This will still work but should be avoided. Please change your scripts
392       to use the "preproc_add" etc functions.
393
394       The following code would check for a call to function 'mysub' and
395       bracket arguments with qw.
396
397         $filter = preproc_add sub {
398            my $str = shift;
399            $str =~ s/^\s+//;  # Strip leading space
400            if ($str =~ /^mysub/) {
401               my ($command, $arguments) = split(/\s+/,$str, 2);
402               $str = "$command qw( $arguments )"
403               if (defined $arguments && $arguments !~ /^qw/);
404            };
405            # Return the input string, modified as required
406            return $str;
407          };
408
409       This would convert:
410
411         pdl> mysub arg1 arg2
412
413       to
414
415         pdl> mysub qw( arg1 arg2 )
416
417       which Perl will understand as a list.  Obviously, a little more effort
418       is required to check for cases where the caller has supplied a normal
419       list (and so does not require automatic quoting) or variable
420       interpolation is required.
421
422       You can remove this preprocessor using the "preproc_del" function which
423       takes one argument (the filter to be removed, it must be the same
424       coderef that was returned from a previous "preproc_add" call):
425
426         pdl> preproc_del $filter;
427
428       An example of actual usage can be found in the "perldl" script. Look at
429       the function "trans" to see how the niceslicing preprocessor is
430       enabled/disabled.
431
432   "perldl" and PDL::NiceSlice
433       PDL::NiceSlice introduces a more convenient slicing syntax for
434       ndarrays. In current versions of "perldl" and "pdl2" niceslicing is
435       enabled by default (if the required CPAN modules are installed on your
436       machine).
437
438       At startup "perldl" will let you know if niceslicing is enabled. The
439       startup message will contain info to this end, something like this:
440
441          perlDL shell v1.XX
442           PDL comes with ABSOLUTELY NO WARRANTY. For details, see the file
443           'COPYING' in the PDL distribution. This is free software and you
444           are welcome to redistribute it under certain conditions, see
445           the same file for details.
446          ReadLines, NiceSlice  enabled
447          Reading /home/csoelle/.perldlrc...
448          Type 'demo' for online demos
449          Loaded PDL v2.XX
450
451       When you get such a message that indicates "NiceSlice" is enabled you
452       can use the enhanced slicing syntax:
453
454         pdl> $x = sequence 10;
455         pdl> p $x(3:8:2)
456
457       For details consult PDL::NiceSlice.
458
459       PDL::NiceSlice installs a filter in the preprocessing pipeline (see
460       above) to enable the enhanced slicing syntax. You can use a few
461       commands in the "perldl" shell to switch this preprocessing on or off
462       and also explicitly check the substitutions that the NiceSlice filter
463       makes.
464
465       You can switch the PDL::NiceSlice filter on and off by typing
466
467         pdl> trans # switch niceslicing on
468
469       and
470
471         pdl> notrans # switch niceslicing off
472
473       respectively. The filter is on by default.
474
475       To see how your commands are translated switch reporting on:
476
477         pdl> report 1;
478         pdl> p $x(3:8:2)
479         processed p $x->slice([3,8,2])
480         [3 5 7]
481
482       Similarly, switch reporting off as needed
483
484         pdl> report 0;
485         pdl>  p $x(3:8:2)
486         [3 5 7]
487
488       Reporting is off by default.
489
490   Automatically execute your own hooks
491       The variable @PERLDL::AUTO is a simple list of perl code strings and/or
492       code reference. It is used to define code to be executed automatically
493       every time the user enters a new line.
494
495       A simple example would be to print the time of each command:
496
497         pdl> push @PERLDL::AUTO,'print scalar(gmtime),"\n"'
498
499         pdl> print zeroes(3,3)
500         Sun May  3 04:49:05 1998
501
502         [
503          [0 0 0]
504          [0 0 0]
505          [0 0 0]
506         ]
507
508         pdl> print "Boo"
509         Sun May  3 04:49:18 1998
510         Boo
511         pdl>
512
513       Or to make sure any changes in the file 'local.perldlrc' are always
514       picked up :-
515
516         pdl> push @PERLDL::AUTO,"do 'local.perldlrc'"
517
518       This code can of course be put *in* 'local.perldlrc', but be careful
519       :-) [Hint: add "unless ($started++)" to above to ensure it only gets
520       done once!]
521
522       Another example application is as a hook for Autoloaders (e.g.
523       PDL::AutoLoader) to add code too which allows them to automatically re-
524       scan their files for changes. This is extremely convenient at the
525       interactive command line. Since this hook is only in the shell it
526       imposes no inefficiency on PDL scripts.
527
528       Finally note this is a very powerful facility - which means it should
529       be used with caution!
530
531
532
533perl v5.34.0                      2022-02-28                         PERLDL(1)
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