NAME¶
Shell::Perl - A read-eval-print loop in Perl
SYNOPSYS¶
use Shell::Perl;
Shell::Perl->run_with_args;
DESCRIPTION¶
This is the implementation of a command-line interpreter for Perl. I wrote this
because I was tired of using
irb when needing a calculator with a real
language within. Ah, that and because it was damn easy to write it.
This module is the heart of the
pirl script provided with
Shell-Perl distribution, along with this module.
EXAMPLE SESSION¶
$ pirl
Welcome to the Perl shell. Type ':help' for more information
pirl @> 1+1
2
pirl @> use YAML qw(Load Dump);
()
pirl @> $data = Load("--- { a: 1, b: [ 1, 2, 3] }\n");
{ a => 1, b => [1, 2, 3] }
pirl @> $var = 'a 1 2 3'; $var =~ /(\w+) (\d+) (\d+)/
("a", 1, 2)
pirl @> :q
COMMANDS¶
Most of the time, the shell reads Perl statements, evaluates them and outputs
the result.
There are a few commands (started by ':') that are handled by the shell itself.
- :h(elp)
- Handy for remembering what the shell commands are.
- :q(uit)
- Leave the shell. The Perl statement "exit" will work too.
SYNONYMS: :exit, :x
- :set out (D|DD|DDS|Y|P)
- Changes the dumper for the expression results used before output. The
current supported are:
- D
- "Data::Dump"
- DD
- "Data::Dumper", the good and old core module
- DDS
- "Data::Dump::Streamer"
- Y
- "YAML"
- P
- a plain dumper ("$ans" or "@ans")
When creating the shell, the dump format is searched among the available ones in
the order "D", "DD", "DDS", "Y" and
"P". That means Data::Dump is preferred and will be used if
available/installed. Otherwise, Data::Dumper is tried, and so on.
Read more about dumpers at Shell::Perl::Dumper.
- :set ctx (scalar|list|void|s|l|v|$|@|_)
- Changes the default context used to evaluate the entered expression. The
default is 'list'.
Intuitively, 'scalar', 's' and '$' are synonyms, just like 'list', 'l', and
'@' or 'void', 'v', '_'.
There is a nice way to override the default context in a given expression.
Just a '#' followed by one of 'scalar|list|void|s|l|v|$|@|_' at the end of
the expression.
pirl @> $var = 'a 1 2 3'; $var =~ /(\w+) (\d+) (\d+)/
("a", 1, 2)
pirl @> $var = 'a 1 2 3'; $var =~ /(\w+) (\d+) (\d+)/ #scalar
1
- :reset
- Resets the environment, erasing the symbols created at the current
evaluation package. See the section "ABOUT EVALUATION".
METHODS¶
Remember this is an alpha version, so the API may change and that includes the
methods documented here. So consider this section as implementation notes for
a while.
In later versions, some of these information may be promoted to a public status.
Others may be hidden or changed and even disappear without further notice.
- new
-
$sh = Shell::Version->new;
The constructor.
- run_with_args
-
Shell::Perl->run_with_args;
Starts the read-eval-print loop after reading options from @ARGV. It is a
class method.
If an option -v or --version is provided, instead of starting
the REPL, it prints the script identification and exits with 0.
$ pirl -v
This is pirl, version 0.0017 (bin/pirl, using Shell::Perl 0.0017)
- run
-
$sh->run;
The same as "run_with_args" but with no code for interpreting
command-line arguments. It is an instance method, so that
"Shell::Perl-"run_with_args> is kind of:
Shell::Perl->new->run;
- eval
-
$answer = $sh->eval($exp);
@answer = $sh->eval($exp);
Evaluates the user input given in $exp as Perl code and returns the result.
That is the 'eval' part of the read-eval-print loop.
- print
-
$sh->print(@args);
Prints a list of args at the output stream currently used by the shell.
- help
-
$sh->help;
Outputs the help as provided by the command ":help".
- reset
-
$sh->reset;
Does nothing by now, but it will.
- dump_history
-
$sh->dump_history();
$sh->dump_history($file);
Prints the readline history to "STDOUT" or the optional file. Used
to implement experimental command ":dump history".
This is experimental code and should change in the future. More control
should be added and integrated with other terminal features.
- set_ctx
-
$sh->set_ctx($context);
Assigns to the current shell context. The argument must be one of " (
'scalar', 'list', 'void', 's', 'l', 'v', '$', '@', '_' ) ".
- set_package
-
$sh->set_package($package);
Changes current evaluation package. Doesn't change if the new package name
is malformed.
- set_out
-
$sh->set_out($dumper);
Changes the current dumper used for printing the evaluation results.
Actually must be one of "D" (for Data::Dump), "DD"
(for Data::Dumper), "DDS" (for Data::Dump::Streamer),
"Y" (for YAML) or "P" (for plain string
interpolation).
- prompt_title
-
$prompt = $sh->prompt_title;
Returns the current prompt which changes with executable name and context.
For example, "pirl @>", "pirl $>", and
"pirl >".
- quit
-
$sh->quit;
This method is invoked when these commands and statements are parsed by the
REPL:
:q
:quit
:x
:exit
quit
exit
It runs the shutdown procedures for a smooth termination of the shell. For
example, it saves the terminal history file.
GORY DETAILS¶
ABOUT EVALUATION¶
When the statement read is evaluated, this is done at a different package, which
is "Shell::Perl::sandbox" by default.
So:
$ perl -Mlib=lib bin/pirl
Welcome to the Perl shell. Type ':help' for more information
pirl @> $a = 2;
2
pirl @> :set out Y # output in YAML
pirl @> \%Shell::Perl::sandbox::
---
BEGIN: !!perl/glob:
PACKAGE: Shell::Perl::sandbox
NAME: BEGIN
a: !!perl/glob:
PACKAGE: Shell::Perl::sandbox
NAME: a
SCALAR: 2
This package serves as an environment for the current shell session and :reset
can wipe it away.
pirl @> :reset
pirl @> \%Shell::Perl::sandbox::
---
BEGIN: !!perl/glob:
PACKAGE: Shell::Perl::sandbox
NAME: BEGIN
TO DO¶
There is a lot to do, as always. Some of the top priority tasks are:
- •
- Accept multiline statements;.
- •
- Refactor the code to promote easy customization of features.
SEE ALSO¶
This project is hosted at Google Code:
http://code.google.com/p/iperl/
To know about interactive Perl interpreters, there are two FAQS contained in
perlfaq3 which are good starting points. Those are
How can I use Perl interactively?
http://perldoc.perl.org/perlfaq3.html#How-can-I-use-Perl-interactively%3f
Is there a Perl shell?
http://perldoc.perl.org/perlfaq3.html#How-can-I-use-Perl-interactively%3f
An extra list of Perl shells can be found here:
http://www.focusresearch.com/gregor/document/psh-1.1.html#other_perl_shells
BUGS¶
It is a one-line evaluator by now.
I don't know what happens if you eval within an eval. I don't expect good things
to come. (Lorn who prodded me about this will going to find it out and then I
will tell you.)
There are some quirks with Term::Readline (at least on Windows).
There are more bugs. I am lazy to collect them all and list them now.
Please report bugs via CPAN RT
<
http://rt.cpan.org/NoAuth/Bugs.html?Dist=Shell-Perl> or
<
mailto://bugs-Shell-Perl@rt.cpan.org>.
AUTHORS¶
Adriano R. Ferreira, <ferreira@cpan.org>
Caio Marcelo, <cmarcelo@gmail.com>
COPYRIGHT AND LICENSE¶
Copyright (C) 2007X2011 by Adriano R. Ferreira
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.