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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 ...

Miscellaneous shell features:


The shell aliases p to be a convenient short form of print, e.g.

   perldl> p ones 5,3

    [1 1 1 1 1]
    [1 1 1 1 1]
    [1 1 1 1 1]

'q' and 'x' are short-hand for quit.

'l' lists the history buffer

'?' is an alias for help

'help', 'apropos', 'usage' and 'sig': all words after these commands are used verbatim and not evaluated by perl. So you can write, e.g.,

    help help  

instead of

    help 'help'


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 this circumstances.


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

$PERLDL::ESCAPE - default value '#'

Any line starting with this character is treated as a shell escape. The default value is chosen because it escapes the code from the standard perl interpreter.

$PERLDL::PAGER - default value more

External program to filter the output of commands. Using more prints output one screenful at a time. On Unix, setting page(1) and $PERLDL::PAGER to tee -a outfile will keep a record of the output generated by subsequent perldl commands (without paging).

$PERLDL::PROMPT - default value 'perldl> '

Enough said But can also be set to a subroutine reference, e.g. $PERLDL::PROMPT = sub {join(':',(gmtime)[2,1,0]).'> '} puts the current time into the prompt.


The user's home directory


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'.


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!

  • 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).

    The variable $PERLDL::PREPROCESS can be set to a code reference (usually in a local configuration file) that will be called, with the current string as argument, just prior to the string being executed by the shell. The modified string should be returned.

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

     $PERLDL::PREPROCESS = 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.

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.
-m module
Unloads the module before processing any user input.
-I directory
Adds directory to the include path. (i.e. the @INC array)




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[ The ultimate metric that I would like to propose for user friendliness is quite simple: if this system was a person, how long would it take before you punched it in the nose.   ]



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