1PERLDL(1) User Contributed Perl Documentation PERLDL(1)
2
6 perldl - Simple shell for PDL (see also pdl2)
7
9 Use PDL interactively:
10 bash$ perldl
12 pdl> $x = sequence(10) # or any other perl or PDL command
13 bash$ pdl
15 pdl> print "Hello, world!\n";
16 Run a script:
18 bash$ cat > pdlscript
20 #!/usr/bin/pdl
21 print "Hello, world!\n";
22 ...
23
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 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 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 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 perldl and pdl support several command-line options, which are
52 discussed near the end of this document.
53 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 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 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 $PERLDL::HISTFILESIZE to change the number of lines saved. The command
72 "l [number]" shows you the last "number" commands you typed where
73 "number" defaults to 20.
74 e.g.:
76 bash$ perldl
78 ReadLines enabled
79 pdl> $x = rfits "foo.fits"
80 BITPIX = -32 size = 88504 pixels
81 Reading 354016 bytes
82 BSCALE = && BZERO =
83 pdl> imag log($x+400)
85 Displaying 299 x 296 image from 4.6939525604248 to 9.67116928100586 ...
86 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 • $_ is not preserved across lines
93 $_ 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 • Scope is not preserved across lines
100 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 NOTE: pdl2 preserves lexical scope between lines.
110 • Execution is immediate
112 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 print "Hello ",
119 "world";
120 prints the phrase "Hello world" in Perl, but (under most
122 circumstances) "Hello " in perldl.
123 • Multi-line execution
125 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 { print "Hello ",
134 "world"; }
135 will print "Hello world" from either Perl or (in multi-line mode)
137 perldl.
138 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 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 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 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 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 pdl> $result = start_lengthy_computation()
167 <Ctrl-C>
168 Ctrl-C detected
169 pdl>
171 Shortcuts and aliases
173 • The shell aliases "p" to be a convenient short form of "print",
174 e.g.
175 pdl> p ones 5,3
177 [
179 [1 1 1 1 1]
180 [1 1 1 1 1]
181 [1 1 1 1 1]
182 ]
183 • "q" and "x" are short-hand for "quit".
185 • "l" lists the history buffer
187 pdl> l # list last 20 commands
189 pdl> l 40 # list last 40 commands
191 • "?" is an alias for help
193 pdl> ? pdl2 # get help for new pdl2 shell
195 • "??" is an alias for apropos
197 pdl> ?? PDL::Doc
199 • 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 pdl> help help
204 instead of
206 pdl> help 'help'
208 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 -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 -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 -f file
224 Loads the file before processing any user input. Any errors during
225 the execution of the file are fatal.
226 -w Runs with warning messages (i.e. the normal perl "-w" warnings)
228 turned-on.
229 -M module
231 Loads the module before processing any user input. Compare
232 corresponding "perl" switch.
233 -m module
235 Unloads the module before processing any user input.
236 -I directory
238 Adds directory to the include path. (i.e. the @INC array) Compare
239 corresponding "perl" switch.
240 -V Prints a summary of PDL config. This information should be included
242 with any PDL bug report. Compare corresponding "perl" switch.
243 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 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 The name is chosen specifically because it was found hidden files were
260 NOT wanted in these circumstances.
261 The startup file should normally include "use PDL::AutoLoader;", as
263 many of the nicer interactive features won't work without it.
264 Shell variables
266 Shell variables: (Note: if you don't like the defaults change them in
267 ~/.perldlrc)
268 • $PERLDL::ESCAPE - default value '#'
270 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 • $PERLDL::HISTFILESIZE - default value 500
276 This is the number of lines of perldl shell command history to
278 keep.
279 • $PERLDL::PAGER - default value "more"
281 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 • $PERLDL::PROMPT - default value 'pdl> '
288 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 • $PERLDL::MULTI - default value 1
294 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 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 Multiline conventional strings and {}, [], and () groupings are
308 well supported.
309 • $PERLDL::NO_EOF - default value 0 / 1 on MSWin32
311 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 • $HOME
320 The user's home directory
322 • $PERLDL::TERM
324 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 • $PDL::toolongtoprint
330 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 Executing scripts from the "perldl" prompt
336 A useful idiom for developing perldl scripts or editing functions on-
337 line is
338 pdl> # emacs script &
340 -- add perldl code to script and save the file
341 pdl> do 'script'
343 -- substitute your favourite window-based editor for 'emacs' (you may
345 also need to change the '&' on non-Unix systems).
346 Running "do 'script'" again updates any variables and function
348 definitions from the current version of 'script'.
349 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 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 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 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 *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 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 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 pdl> preproc_add $myfilter unless preproc_registered $myfilter;
389 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 The following code would check for a call to function 'mysub' and
395 bracket arguments with qw.
396 $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 This would convert:
410 pdl> mysub arg1 arg2
412 to
414 pdl> mysub qw( arg1 arg2 )
416 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 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 pdl> preproc_del $filter;
427 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 "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 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 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 When you get such a message that indicates "NiceSlice" is enabled you
452 can use the enhanced slicing syntax:
453 pdl> $x = sequence 10;
455 pdl> p $x(3:8:2)
456 For details consult PDL::NiceSlice.
458 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 You can switch the PDL::NiceSlice filter on and off by typing
466 pdl> trans # switch niceslicing on
468 and
470 pdl> notrans # switch niceslicing off
472 respectively. The filter is on by default.
474 To see how your commands are translated switch reporting on:
476 pdl> report 1;
478 pdl> p $x(3:8:2)
479 processed p $x->nslice([3,8,2])
480 [3 5 7]
481 Similarly, switch reporting off as needed
483 pdl> report 0;
485 pdl> p $x(3:8:2)
486 [3 5 7]
487 Reporting is off by default.
489 Automatically execute your own hooks
491 The variable @PERLDL::AUTO is a simple list of perl code strings and/or
492 code reference. It is used to define code to be executed automatically
493 every time the user enters a new line.
494 A simple example would be to print the time of each command:
496 pdl> push @PERLDL::AUTO,'print scalar(gmtime),"\n"'
498 pdl> print zeroes(3,3)
500 Sun May 3 04:49:05 1998
501 [
503 [0 0 0]
504 [0 0 0]
505 [0 0 0]
506 ]
507 pdl> print "Boo"
509 Sun May 3 04:49:18 1998
510 Boo
511 pdl>
512 Or to make sure any changes in the file 'local.perldlrc' are always
514 picked up :-
515 pdl> push @PERLDL::AUTO,"do 'local.perldlrc'"
517 This code can of course be put *in* 'local.perldlrc', but be careful
519 :-) [Hint: add "unless ($started++)" to above to ensure it only gets
520 done once!]
521 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 Finally note this is a very powerful facility - which means it should
529 be used with caution!
530perl v5.34.0 2021-08-16 PERLDL(1)