How can I start an interactive console for Perl?

Question

How can I start an interactive console for Perl, similar to the irb command for Ruby or python for Python?

Answer 1

^{Update: I've since created a downloadable REPL - see my other answer.}

With the benefit of hindsight:

• The third-party solutions mentioned among the existing answers are either cumbersome to install and/or do not work without non-trivial, non-obvious additional steps - some solutions appear to be at least half-abandoned.
• A usable REPL needs the readline library for command-line-editing keyboard support and history support - ensuring this is a trouble spot for many third-party solutions.
• If you install CLI rlwrap, which provides readline support to any command, you can combine it with a simple Perl command to create a usable REPL, and thus make do without third-party REPL solutions.
  • On OSX, you can install rlwrap via Homebrew with brew install rlwrap.
  • Linux distros should offer rlwrap via their respective package managers; e.g., on Ubuntu, use sudo apt-get install rlwrap.
  • See Ján Sáreník's answer for said combination of rlwrap and a Perl command.

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What you do NOT get with Ján's answer:

• auto-completion
• ability to enter multi-line statements

The only third-party solution that offers these (with non-trivial installation + additional, non-obvious steps), is psh, but:

• it hasn't seen activity in around 2.5 years

• its focus is different in that it aims to be a full-fledged shell replacement, and thus works like a traditional shell, which means that it doesn't automatically evaluate a command as a Perl statement, and requires an explicit output command such as print to print the result of an expression.

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Ján Sáreník's answer can be improved in one way:

• By default, it prints arrays/lists/hashtables as scalars, i.e., only prints their element count, whereas it would be handy to enumerate their elements instead.

If you install the Data::Printer module with [sudo] cpan Data::Printer as a one-time operation, you can load it into the REPL for use of the p() function, to which you can pass lists/arrays/hashtables for enumeration.

Here's an alias named iperl with readline and Data::Printer support, which can you put in your POSIX-like shell's initialization file (e.g., ~/.bashrc):

alias iperl='rlwrap -A -S "iperl> " perl -MData::Printer -wnE '\''BEGIN { say "# Use `p @` or `p %` to print arrays/lists/hashtables; e.g.: `p %ENV`"; } say eval()//$@'\'

E.g., you can then do the following to print all environment variables via hashtable %ENV:

$ iperl        # start the REPL
iperl> p %ENV  # print key-value pairs in hashtable %ENV

As with Ján's answer, the scalar result of an expression is automatically printed; e.g.:

iperl> 22 / 7  # automatically print scalar result of expression: 3.14285714285714