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:
- -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. 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!