perldl - Simple shell for PDL


perldl - Simple shell for PDL


        %> perldl
        perldl> $a=sequence(10) # or any other PDL command


The program perldl is a simple shell (written in perl) for interactive use of PDL. perl/PDL commands can simply be typed in - and edited if you have appropriate version of the ReadLines and ReadKeys modules installed. In that case perldl also supports a history mechanism where the last 50 commands are always stored in the file .perldl_hist in your home directory between sessions. The command l [number] shows you the last number commands you typed where number defaults to 20.


   % perldl
   ReadLines enabled
   perldl> $a = rfits "foo.fits"
   BITPIX =  -32  size = 88504 pixels
   Reading  354016 bytes
   BSCALE =  &&  BZERO =
   perldl> imag log($a+400)
   Displaying 299 x 296 image from 4.6939525604248 to 9.67116928100586 ...

Command-line options

Load Tk when starting the shell (the perl Tk module, which is available from CPAN must be installed). This enables readline event loop processing.

-f file
Loads the file before processing any user input. Any errors during the execution of the file are fatal.

Runs with warning messages (i.e. the normal perl -w warnings) turned-on.

-M module
Loads the module before processing any user input. Compare corresponding perl switch.

-m module
Unloads the module before processing any user input.

-I directory
Adds directory to the include path. (i.e. the @INC array) Compare corresponding perl switch.

Prints a summary of PDL config. This information should be included with any PDL bug report. Compare corresponding perl switch.

Terminating perldl

A perldl session can be terminated with any of the commands quit, exit or the shorthands x or q.

Terminating commands (Ctrl-C handling)

Commands executed within perldl can be terminated prematurely using Ctrl-C (or whichever key sequence sends an INT signal to the process on your terminal). Provided your PDL code does not ignore sigints this should throw you back at the perldl command prompt:

  perldl> $result = start_lengthy_computation()
 Ctrl-C detected

Shortcuts and aliases

The startup file ~/.perldlrc

If the file ~/.perldlrc is found it is sourced at start-up to load default modules, set shell variables, etc. If it is NOT found the distribution file PDL/default.perldlrc is read instead. This loads various modules considered useful by default, and which ensure compatibility with v1.11. If you don't like this and want a more streamlined set of your own favourite modules simple create your own ~/.perldlrc

To set even more local defaults the file local.perldlrc (in the current directory) is sourced if found. This lets you load modules and define subroutines for the project in the current directory.

The name is chosen specfically because it was found hidden files were NOT wanted in these circumstances.

Shell variables

Shell variables: (Note: if you don't like the defaults change them in ~/.perldlrc)

Executing scripts from the perldl prompt

A useful idiom for developing perldl scripts or editing functions on-line is

      perldl> # emacs script &
                      -- add perldl code to script and save the file
      perldl> do 'script'

-- substitute your favourite window-based editor for 'emacs' (you may also need to change the '&' on non-Unix systems).

Running ``do 'script''' again updates any variables and function definitions from the current version of 'script'.

Automatically execute your own hooks

The variable @PERLDL::AUTO is a simple list of perl code strings and/or code reference. It is used to define code to be executed automatically every time the user enters a new line.

A simple example would be to print the time of each command:

 perldl> push @PERLDL::AUTO,'print scalar(gmtime),"\n"'
 perldl> print zeroes(3,3)
 Sun May  3 04:49:05 1998
  [0 0 0]
  [0 0 0]
  [0 0 0]
 perldl> print "Boo"
 Sun May  3 04:49:18 1998

Or to make sure any changes in the file 'local.perldlrc' are always picked up :-

 perldl> push @PERLDL::AUTO,"do 'local.perldlrc'"

This code can of course be put *in* 'local.perldlrc', but be careful :-) [Hint: add unless ($started++) to above to ensure it only gets done once!]

Another example application is as a hook for Autoloaders (e.g. PDL::AutoLoader) to add code too which allows them to automatically re-scan their files for changes. This is extremely convenient at the interactive command line. Since this hook is only in the shell it imposes no inefficiency on PDL scripts.

Finally note this is a very powerful facility - which means it should be used with caution!

Command preprocessing

NOTE: This feature is used by default by PDL::NiceSlice. See below for more about slicing at the perldl prompt

In some cases, it is convenient to process commands before they are sent to perl for execution. For example, this is the case where the shell is being presented to people unfamiliar with perl but who wish to take advantage of commands added locally (eg by automatically quoting arguments to certain commands).

*NOTE*: The preprocessing interface has changed from earlier versions! The old way using $PERLDL::PREPROCESS will still work but is strongly deprecated and might go away in the future.

You can enable preprocessing by registering a filter with the preproc_add function. preproc_add takes one argument which is the filter to be installed. A filter is a Perl code reference (usually set in a local configuration file) that will be called, with the current command string as argument, just prior to the string being executed by the shell. The modified string should be returned. Note that you can make perldl completely unusable if you fail to return the modified string; quitting is then your only option.

Filters can be removed from the preprocessing pipeline by calling preproc_del with the filter to be removed as argument. To find out if a filter is currently installed in the preprocessing pipeline use preproc_registered:

  perldl> preproc_add $myfilter unless preproc_registered $myfilter;

Previous versions of perldl used the variable $PERLDL::PREPROCESS. This will still work but should be avoided. Please change your scripts to use the preproc_add etc functions.

The following code would check for a call to function 'mysub' and bracket arguments with qw.

 $filter = preproc_add sub {
   my $str = shift;
   $str =~ s/^\s+//;  # Strip leading space
   if ($str =~ /^mysub/) {
     my ($command, $arguments) = split(/\s+/,$str, 2);
     $str = "$command qw( $arguments )" 
       if (defined $arguments && $arguments !~ /^qw/);
   # Return the input string, modified as required
   return $str;

This would convert:

  perldl> mysub arg1 arg2


  perldl> mysub qw( arg1 arg2 )

which Perl will understand as a list. Obviously, a little more effort is required to check for cases where the caller has supplied a normal list (and so does not require automatic quoting) or variable interpolation is required.

You can remove this preprocessor using the preproc_del function which takes one argument (the filter to be removed, it must be the same coderef that was returned from a previous preproc_add call):

  perldl> preproc_del $filter;

An example of actual usage can be found in the perldl script. Look at the function trans to see how the niceslicing preprocessor is enabled/disabled.

perldl and PDL::NiceSlice

PDL::NiceSlice introduces a more convenient slicing syntax for piddles. In current versions of perldl niceslicing is enabled by default (if the required CPAN modules are installed on your machine).

At startup perldl will let you know if niceslicing is enabled. The startup message will contain info to this end, something like this:

   perlDL shell v1.XX
    PDL comes with ABSOLUTELY NO WARRANTY. For details, see the file
    'COPYING' in the PDL distribution. This is free software and you
    are welcome to redistribute it under certain conditions, see
    the same file for details.
   ReadLines, NiceSlice  enabled
   Reading /home/csoelle/.perldlrc...
   Type 'demo' for online demos
   Loaded PDL v2.XX

When you get such a message that indicates NiceSlice is enabled you can use the enhanced slicing syntax:

  perldl> $a = sequence 10;
  perldl> p $a(3:8:2)

For details consult the PDL::NiceSlice manpage.

PDL::NiceSlice installs a filter in the preprocessing pipeline (see above) to enable the enhanced slicing syntax. You can use a few commands in the perldl shell to switch this preprocessing on or off and also explicitly check the substitutions that the NiceSlice filter makes.

You can switch the PDL::NiceSlice filter on and off by typing

  perldl> trans # switch niceslicing on


  perldl> notrans # switch niceslicing off

respectively. The filter is on by default.

To see how your commands are translated switch reporting on:

  perldl> report 1;
  perldl> p $a(3:8:2)
 processed p $a->nslice([3,8,2])
 [3 5 7]

Similarly, switch reporting off as needed

  perldl> report 0;
  perldl>  p $a(3:8:2)
 [3 5 7]

Reporting is off by default.

 perldl - Simple shell for PDL