pdl 1:2.4.7+dfsg-2ubuntu5 / usr / lib / perl5 / PDL / perldl.pod

=head1 NAME

  perldl - Simple shell for PDL (also see pdl2)


=head1 SYNOPSIS

Use PDL interactively:

  bash$ perldl
  pdl> $a = sequence(10) # or any other perl or PDL command
  
  bash$ pdl
  pdl> print "Hello, world!\n"; 

Run a script:

  bash$ cat > pdlscript
  #!/usr/bin/pdl
  print "Hello, world!\n";
  ...


=head1 DESCRIPTION

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

The B<perldl> shell runs an initial startup file (C<~/.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, B<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.

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

=head2 Reference manual & online help

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

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

=head2 History mechanism

If you have the perl modules ReadLines and ReadKeys installed, then
B<perldl> supports a history and line-editing mechanism using editing
keys similar to L<emacs(1)>. The last 50 commands are always stored in
the file F<.perldl_hist> in your home directory between sessions.
Set C<$PERLDL::HISTFILESIZE> to change the number of lines saved.
The command C<l [number]> shows you the last C<number> commands you
typed where C<number> defaults to 20.

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 ...

=head2 Command execution

If you enter a simple command at the B<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:

=over 3

=item * $_ 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.

=item * Scope is not preserved across lines

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

=item * 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 C<Hello world> in Perl, but (under most circumstances) 
C<Hello > in B<perldl>. 

=item * Multi-line execution

In multiline mode (which is enabled by default, see B<Shell
variables>, below), B<perldl> searches for searches for block-like
constructs with curly braces, parentheses, quotes, and related
delimiters.  If you leave such a construct open, B<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)
B<perldl>.  

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

=back

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 B<pdl> instead of B<perl>
as the interpreter in the script's initial shebang line.


=head2 Terminating C<perldl>

A C<perldl> session can be terminated with any of the commands
C<quit>, C<exit> or the shorthands C<x> or C<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 B<perldl>.

=head2 Terminating commands (Ctrl-C handling)

Commands executed within C<perldl> can be terminated prematurely
using C<Ctrl-C> (or whichever key sequence sends an INT signal
to the process on your terminal). Provided your PDL code does not
ignore C<sigint>s this should throw you back at the C<perldl>
command prompt:

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

  pdl>

=head2 Shortcuts and aliases

=over

=item *

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

   pdl> p ones 5,3

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

=item *

C<q> and C<x> are short-hand for C<quit>.

=item *

C<l> lists the history buffer

  pdl> l # list last 20 commands

  pdl> l 40 # list last 40 commands

=item *

C<?> is an alias for L<help|PDL::Doc::Perldl/help>

  pdl> ? pdl2    # get help for new pdl2 shell

=item *

C<??> is an alias for L<apropos|PDL::Doc::Perldl/apropos>

  pdl> ?? PDL::Doc

=item *

L<help|PDL::Doc::Perldl/help>, L<apropos|PDL::Doc::Perldl/apropos>,
L<usage|PDL::Doc::Perldl/usage> and L<sig|PDL::Doc::Perldl/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'

=back


=head2 Command-line options

B<perldl> and B<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 B<perldlE<gt>>
prompt.  They are:

=over 4

=item -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.

=item -f file

Loads the file before processing any user input. Any errors
during the execution of the file are fatal.

=item -w

Runs with warning messages (i.e. the normal perl C<-w> warnings)
turned-on.

=item -M module

Loads the module before processing any user input.
Compare corresponding C<perl> switch.

=item -m module

Unloads the module before processing any user input.

=item -I directory

Adds directory to the include path. (i.e. the @INC array)
Compare corresponding C<perl> switch.

=item -V

Prints a summary of PDL config. This information should
be included with any PDL bug report. Compare corresponding
C<perl> switch.

=back

=head2 The startup file F<~/.perldlrc>

If the file F<~/.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
F<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 F<~/.perldlrc>.  You may
wish to start from the existing F<PDL/default.perldlrc> as a template
since it will not be sourced once you replace it with your own version.

To set even more local defaults the file  F<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.

=head2 Shell variables

Shell variables: (I<Note>: if you don't like the defaults change
them in F<~/.perldlrc>)

=over

=item *

$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.

=item *

$PERLDL::HISTFILESIZE  - default value 500

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

=item *

$PERLDL::PAGER - default value C<more>

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

=item *

$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.

=item *

$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 C<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.

=item *

$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.


=item *

$HOME

The user's home directory

=item *

$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.

=back

=head2 Executing scripts from the C<perldl> prompt

A useful idiom for developing perldl scripts or editing functions
on-line is

  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'.

=head2 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.

=head2 Command preprocessing

NOTE: This feature is used by default by L<PDL::NiceSlice|PDL::NiceSlice>.
See below for more about slicing at the C<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).

*I<NOTE>*: The preprocessing interface has changed from earlier
versions! The old way using C<$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
C<preproc_add> function. C<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 C<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
C<preproc_del> with the filter to be removed as argument.  To find out
if a filter is currently installed in the preprocessing pipeline use
C<preproc_registered>:

  pdl> preproc_add $myfilter unless preproc_registered $myfilter;

Previous versions of C<perldl> used the variable C<$PERLDL::PREPROCESS>.
This will still work but should be avoided. Please change your scripts
to use the C<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 C<preproc_del> function
which takes one argument (the filter to be removed, it must be the
same coderef that was returned from a previous C<preproc_add> call):

  pdl> preproc_del $filter;

An example of actual usage can be found in the C<perldl> script. Look
at the function C<trans> to see how the niceslicing preprocessor is
enabled/disabled.

=head2 C<perldl> and L<PDL::NiceSlice|PDL::NiceSlice>

L<PDL::NiceSlice|PDL::NiceSlice> introduces a more convenient
slicing syntax for piddles. In current versions of C<perldl>
niceslicing is enabled by default (if the required CPAN modules
are installed on your machine).

At startup C<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 C<NiceSlice> is enabled
you can use the enhanced slicing syntax:

  pdl> $a = sequence 10;
  pdl> p $a(3:8:2)

For details consult L<PDL::NiceSlice>.

L<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 C<perldl> shell to
switch this preprocessing on or off and also explicitly check
the substitutions that the NiceSlice filter makes.

You can switch the L<PDL::NiceSlice|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.

=head2 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:

  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 C<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!