Reference manual & online help

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

e.g.:

   bash$ perldl
   ReadLines enabled
   pdl> $a = rfits "foo.fits"
   BITPIX =  -32  size = 88504 pixels
   Reading  354016 bytes
   BSCALE =  &&  BZERO =

   pdl> imag log($a+400)
   Displaying 299 x 296 image from 4.6939525604248 to 9.67116928100586 ...

Command execution

• $_ 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).

    NOTE: pdl2 preserves lexical scope between lines.
      

• 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 explicitly 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"

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)

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

  pdl>

Shortcuts and aliases

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

     pdl> 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

    pdl> l # list last 20 commands
  
    pdl> l 40 # list last 40 commands
      

• "?" is an alias for help

    pdl> ? pdl2    # get help for new pdl2 shell
      

• "??" is an alias for apropos

    pdl> ?? 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.,

    pdl> help help
      

  instead of

    pdl> help 'help'
      

Command-line options

-glut

Load OpenGL when starting the shell (the perl OpenGL module, which is available from CPAN must be installed). This enables readline event loop processing. Don't use with -tk.

-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. Don't use with -glut.

-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

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 specifically 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

• $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::HISTFILESIZE - default value 500

  This is the number of lines of perldl shell command history to keep.

• $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 'pdl> '

  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 / 1 on MSWin32

  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.

• $PDL::toolongtoprint

  The maximal size pdls to print (defaults to 10,000 elements). This is not just a "perldl" or "pdl2" variable but it is something that is usually needed in an interactive debugging session.

Executing scripts from the "perldl" prompt

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

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

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":

  pdl> 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:

  pdl> mysub arg1 arg2

to

  pdl> 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):

  pdl> 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

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:

  pdl> $a = sequence 10;
  pdl> 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

  pdl> trans # switch niceslicing on

and

  pdl> notrans # switch niceslicing off

respectively. The filter is on by default.

To see how your commands are translated switch reporting on:

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

Similarly, switch reporting off as needed

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

Reporting is off by default.

Automatically execute your own hooks

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

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

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

  pdl> 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!