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PERLDL(1)		       User Contributed Perl Documentation			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" com-
       mands 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 short-
       hands "x" or "q".

       Terminating commands (Ctrl-C handling)

       Commands executed within "perldl" can be terminated prematurely using "Ctrl-C" (or which-
       ever 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

       o   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]
	      ]

       o   "q" and "x" are short-hand for "quit".

       o   "l" lists the history buffer

	     perldl> l # list last 20 commands

	     perldl> l 40 # list last 40 commands

       o   "?" is an alias for help

	     perldl> ? wpic

       o   "??" is an alias for apropos

	     perldl> ?? PDL::Doc

       o   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)

       o   $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.

       o   $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 pag-
	   ing).

       o   $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.

       o   $HOME

	   The user's home directory

       o   $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 cur-
       rent 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 cau-
       tion!

       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 exe-
       cution. For example, this is the case where the shell is being presented to people unfa-
       miliar with perl but who wish to take advantage of commands added locally (eg by automati-
       cally 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 unus-
       able 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 auto-
       matic 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 ver-
       sions 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.

perl v5.8.0				    2003-01-29					PERLDL(1)
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