Devel::REPL - a modern perl interactive shell
my $repl = Devel::REPL->new;
$repl->load_plugin($_) for qw(History LexEnv);
Alternatively, use the 're.pl' script installed with the distribution
This is an interactive shell for Perl, commonly known as a REPL - Read, Evaluate, Print, Loop. The shell provides for rapid development or testing of code without the need to create a temporary source code file.
Through a plugin system, many features are available on demand. You can also tailor the environment through the use of profiles and run control files, for example to pre-load certain Perl modules when working on a particular project.
To start a shell, follow one of the examples in the "SYNOPSIS" above.
Once running, the shell accepts and will attempt to execute any code given. If the code executes successfully you'll be shown the result, otherwise an error message will be returned. Here are a few examples:
$_ print "Hello, world!\n"
Compile error: Bareword "nosuchfunction" not allowed while "strict subs" in use at (eval 130) line 5.
In the first example above you see the output of the command (Hello, world!), if any, and then the return value of the statement (1). Following that example, an error is returned when the execution of some code fails.
Note that the lack of semicolon on the end is not a mistake - the code is run inside a Block structure (to protect the REPL in case the code blows up), which means a single statement doesn't require the semicolon. You can add one if you like, though.
If you followed the first example in the "SYNOPSIS" above, you'll have the History and LexEnv plugins loaded (and there are many more available). Although the shell might support "up-arrow" history, the History plugin adds "bang" history to that so you can re-execute chosen commands (with e.g. !53). The LexEnv plugin ensures that lexical variables declared with the my keyword will automatically persist between statements executed in the REPL shell.
When you use any Perl module, the import() will work as expected - the exported functions from that module are available for immediate use:
$_ carp "I'm dieeeing!\n"
String found where operator expected at (eval 129) line 5, near "carp "I'm dieeeing!\n""
(Do you need to predeclare carp?)
Compile error: syntax error at (eval 129) line 5, near "carp "I'm dieeeing!\n""
BEGIN not safe after errors--compilation aborted at (eval 129) line 5.
$_ use Carp
$_ carp "I'm dieeeing!\n"
at /usr/share/perl5/Lexical/Persistence.pm line 327
To quit from the shell, hit control+d or control+c.
For particular projects you might well end up running the same commands each time the REPL shell starts up - loading Perl modules, setting configuration, and so on. A run control file lets you have this done automatically, and you can have multiple files for different projects.
By default the re.pl program looks for $HOME/.re.pl/repl.rc, and runs whatever code is in there as if you had entered it at the REPL shell yourself.
To set a new run control file that's also in that directory, pass it as a filename like so:
system$ re.pl --rcfile myproject.pc
If the filename happens to contain a forwardslash, then it's used absolutely, or realive to the current working directory:
system$ re.pl --rcfile /path/to/my/project/repl.rc
Within the run control file you might want to load plugins. This is covered in "The REPL shell object" section, below.
To allow for the sharing of run control files, you can fashion them into a Perl module for distribution (perhaps via the CPAN). For more information on this feature, please see the Devel::REPL::Profile manual page.
A default profile ships with Devel::REPL; it loads the following plugins:
Plugins are a way to add funcionality to the REPL shell, and take advantage of Devel::REPL being based on the Moose object system for Perl 5. This means it's simple to 'hook into' many steps of the R-E-P-L process. Plugins can change the way commands are interpreted, or the way their results are output, or even add commands to the shell environment.
A number of plugins ship with Devel::REPL, and more are available on the CPAN. Some of the shipped plugins are loaded in the default profile, mentioned above.
Writing your own plugins is not difficult, and is discussed in the Devel::REPL::Plugin manual page, along with links to the manual pages of all the plugins shipped with Devel::REPL.
From time to time you'll want to interact with or manipulate the Devel::REPL shell object itself; that is, the instance of the shell you're currently running.
The object is always available through the $_REPL variable. One common requirement is to load an additional plugin, after your profile and run control files have already been executed:
$_ print "Hello again, world!\n"
Hello again, world!
Took 0.00148296356201172 seconds.
In addition to the contents of the standard Perl distribution, you will need the following:
Moose >= 0.64
MooseX::Object::Pluggable >= 0.0009
MooseX::Getopt >= 0.15
MooseX::AttributeHelpers >= 0.14
Optionally, some plugins if installed will require the following modules:
Matt S Trout - mst (at) shadowcatsystems.co.uk (http://www.shadowcatsystems.co.uk/)
This library is free software under the same terms as perl itself
To install Devel::REPL, copy and paste the appropriate command in to your terminal.
perl -MCPAN -e shell
For more information on module installation, please visit the detailed CPAN module installation guide.