perldlp - Online in the Cloud

PROGRAM:

NAME

perldl - Simple shell for PDL (see also pdl2)

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";
...

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. The last 500
commands are always stored in the file .perldl_hist in your home directory between
sessions. Set $PERLDL::HISTFILESIZE to change the number of lines saved. The command "l
[number]" shows you the last "number" commands you typed where "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 ...

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).

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 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:

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
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 pdl> prompt. They are:

-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
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. You may wish to start from the
existing 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 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::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
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'.

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":

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
PDL::NiceSlice introduces a more convenient slicing syntax for piddles. In current
versions of "perldl" and "pdl2" 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:

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
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
"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!

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