PERLDL(1)

NAME
perldl - Simple shell for PDL

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

DESCRIPTION
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.

e.g.:

   % 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

-tk 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.

-w  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.

-V  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 "sigint"s this should throw you back at the "perldl" command prompt:

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

  perldl>

  Shortcuts and aliases

•   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

      perldl> l # list last 20 commands

      perldl> l 40 # list last 40 commands

•   "?" is an alias for help

      perldl> ? wpic

•   "??" is an alias for apropos

      perldl> ?? PDL::Doc

•   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'

  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)

•   $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.

•   $PERLDL::MULTI - default value 1

    If this is set to a true value, then perldl will parse multi-line perl blocks: your input will not be executed until you finish a line with no outstanding group operators (such as quotes, blocks, parenthesis, or brackets) still active. Continuation lines have a different prompt that shows you what delimiters are still active.

    Note that this is not (yet!) a complete perl parser. In particular, Text::Balanced appears to be able to ignore quoting operatores like "q/ ... /" within a line, but not to be able to extend them across lines. Likewise, there is no support for the '<<' operator.

    Multiline conventional strings and {}, [], and () groupings are well supported.

•   $PERLDL::NO_EOF - default value 0

    Protects against accidental use of "^D" from the terminal. If this is set to a true value, then you can't accidentally exit perldl by typing "^D". If you set it to a value larger than 1 (and PERLDL::MULTI is set), then you can't use "^D" to exit multiline commands either. If you're piping commands in from a file or pipe, this variable has no effect.

•   $HOME

    The user's home directory

•   $PERLDL::TERM

    This is the Term::ReadLine object associated with the perldl shell. It can be used by routines called from perldl if your command is interactive.

  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
 Boo
 perldl>

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

to

  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 PDL::NiceSlice.

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

and

  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.