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PERLDL(1)	      User Contributed Perl Documentation	     PERLDL(1)

NAME
       perldl - Simple shell for PDL

SYNOPSIS
	       Use PDL interactively:

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

		       %> pdl
		       perldl> print "Hello, world!\n";

	       Run a script:

		       %> perldl - pdlscript

		       #!/usr/bin/pdl

DESCRIPTION
       The program perldl is a simple shell (written in perl) for interactive
       use of PDL.  It consists of a command-line interface that supports
       immediate interpretation of perl commands and expressions.  Perl
       expressions, including PDL constructs, can be entered directly at the
       keyboard and are compiled and executed immediately.  The syntax is not
       exactly identical to Perl, in that under most circumstances ending a
       line causes immediate execution of the command entered so far (no
       trailing ';' is required).

       The synonym pdl is a compiled executable that is useful as a script
       interpreter using UNIX shebang ("#!") syntax.  This is useful for
       generating and re-executing command-journal files from perldl.

       The perldl shell runs an initial startup file ("~/.perldlrc") that can
       be used to pre-load perl modules or configure the global perl
       environment.  It features a path mechanism for autoloading perl
       subroutines.  There is a command-history mechanism, and several other
       useful features such as command preprocessing, shortcuts for commonly
       used commands such as "print", and the ability to execute arbitrary
       code whenever a prompt is printed.

       Depending on your configuration settings, perldl can be set to honor or
       ignore the ^D (end-of-file) character when sent from a terminal, or to
       attempt to do the Right Thing when a block construct spanning multiple
       lines is encountered.

       perldl and pdl support several command-line options, which are
       discussed near the end of this document.

       Reference manual & online help

       The PDL reference manual and online help are available from within
       perldl, using the help and apropos commands (which may also be
       abbreviated ? and ??.)	The help command alone prints a summary of
       help syntax, and help  <module-name> will print POD documentation from
       the module you mention (POD is the Perl format for embedding
       documentation in your perl code; see perlpod for details).

       If you include POD documentation in your autoload subroutines (see path
       mechanism below), then both help and apropos will find it and be able
       to format and display it on demand.

       History mechanism

       If you have the perl modules ReadLines and ReadKeys installed, then
       perldl supports a history and line-editing mechanism using editing keys
       similar to emacs(1). 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 execution

       If you enter a simple command at the perldl command line, it is
       immediately executed in a Perl eval().  The environment is almost
       identical to that within a perl script, with some important exceptions:

       ·  $_ is not preserved across lines

	  $_ is used to hold the command line for initial processing, so at
	  the beginning of processing of each command line, $_ contains the
	  command itself.  Use variables other than $_ to store values across
	  lines.

       ·  Scope is not preserved across lines

	  Each command line is executed in a separate "eval" block within
	  perl, so scoping commands such as "my" and "local" may not perform
	  exactly as expected -- in particular, if you declare a variable with
	  "my", it is local to the particular command line on which you typed
	  the "my" command, which means that it will evaporate before the next
	  prompt is printed.  (You can use "my" variables in a multi-line
	  block or to isolate values within a single command line, of course).

       ·  Execution is immediate

	  Under most circumstances, as soon as you end a line of input the
	  line is parsed and executed.	This breaks Perl's normal dependence
	  on semicolons as command delimiters.	For example, the two-line
	  expression

	    print "Hello ",
	       "world";

	  prints the phrase "Hello world" in Perl, but (under most
	  circumstances) "Hello " in perldl.

       ·  Multi-line execution

	  In multiline mode (which is enabled by default, see Shell variables,
	  below), perldl searches for searches for block-like constructs with
	  curly braces, parentheses, quotes, and related delimiters.  If you
	  leave such a construct open, perldl accepts more lines of input
	  until you close the construct or explictly end the multi-line
	  expression with ^D.	Following the example above, the phrase

	    { print "Hello ",
		 "world"; }

	  will print "Hello world" from either Perl or (in multi-line mode)
	  perldl.

	  Warning: The multi-line parsing uses Damian Conway's Text::Balanced
	  module, which contains some flaws -- so it can be fooled by quote-
	  like operators such as "q/.../", included POD documentation, multi-
	  line "<<" quotes, and some particularly bizarre-but-valid "m/.../"
	  matches and "s/.../.../" substitutions.  In such cases, use ^D to
	  close out the multi-line construct and force compilation-and-
	  execution.

       If you want to preserve this behavior in a script (for example to
       replay a command journal file; see below on how to create one), you can
       use pdl instead of perl as the interpreter in the script's initial
       shebang line.

       Terminating "perldl"

       A "perldl" session can be terminated with any of the commands "quit",
       "exit" or the shorthands "x" or "q".  If EOF handling is switched on
       (the default) you can also type ^D at the command prompt.

       If the command input is NOT a terminal (for example if you are running
       from a command journal file), then EOF will always terminate perldl.

       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'

       Command-line options

       perldl and pdl support several command-line options to adjust the
       behavior of the session.	 Most of them are equivalent to commands that
       can be entered at the perldl> prompt.  They are:

       -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.

       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.

       The startup file should normally include "use PDL::AutoLoader;", as
       many of the nicer interactive features won't work without it.

       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'.

       Executing perldl scripts from the command line

       PDL scripts are just perl scripts that happen to use PDL (and possibly
       PDL::NiceSlice).	 But for the truly lazy, perldl can be invokes as a
       script interpreter.  Because perldl is itself an interpreted perl
       script, most unices won't allow you to say "#!/usr/bin/perldl" at the
       top of your script.

       Instead, say "#!/usr/bin/pdl" and your script will be executed exactly
       as if you typed it, line-by-line, into the perldl shell.

       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.

       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!

perl v5.10.0			  2008-08-29			     PERLDL(1)
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