How can I start an interactive console for Perl?

Question

You can use the perl debugger on a trivial program, like so:

perl -de1

Alternatively there's Alexis Sukrieh's Perl Console application, but I haven't used it.

Not only did Matt Trout write an article about a REPL, he actually wrote one - Devel::REPL

I've used it a bit and it works fairly well, and it's under active development.

BTW, I have no idea why someone modded down the person who mentioned using "perl -e" from the console. This isn't really a REPL, true, but it's fantastically useful, and I use it all the time.

I wrote a script I call "psh":

#! /usr/bin/perl

while (<>) {
  chomp;
  my $result = eval;
  print "$_ = $result\n";
}

Whatever you type in, it evaluates in Perl:

> gmtime(2**30)
gmtime(2**30) = Sat Jan 10 13:37:04 2004

> $x = 'foo'
$x = 'foo' = foo

> $x =~ s/o/a/g
$x =~ s/o/a/g = 2

> $x
$x = faa

If you want history, use rlwrap. This could be your ~/bin/ips for example:

#!/bin/sh
echo 'This is Interactive Perl shell'
rlwrap -A -pgreen -S"perl> " perl -wnE'say eval()//$@'

And this is how it looks like:

$ ips
This is Interactive Perl shell
perl> 2**128
3.40282366920938e+38
perl> 

I think you're asking about a REPL (Read, Evaluate, Print, Loop) interface to perl. There are a few ways to do this:

• Matt Trout has an article that describes how to write one
• Adriano Ferreira has described some options
• and finally, you can hop on IRC at irc.perl.org and try out one of the eval bots in many of the popular channels. They will evaluate chunks of perl that you pass to them.

I use the command line as a console:

$ perl -e 'print "JAPH\n"'

Then I can use my bash history to get back old commands. This does not preserve state, however.

This form is most useful when you want to test "one little thing" (like when answering Perl questions). Often, I find these commands get scraped verbatim into a shell script or makefile.