How can I convert Perl one-liners into complete scripts?

Question

I find a lot of Perl one-liners online. Sometimes I want to convert these one-liners into a script, because otherwise I\'ll forget the syntax of the one-liner.

For e

Answer 1

That one's really easy to store in a script!

#! /usr/bin/perl -p
s/(\d+)/localtime($1)/e

The -e option introduces Perl code to be executed—which you might think of as a script on the command line—so drop it and stick the code in the body. Leave -p in the shebang (#!) line.

In general, it's safest to stick to at most one "clump" of options in the shebang line. If you need more, you could always throw their equivalents inside a BEGIN {} block.

Don't forget chmod +x ~/bin/nagiostime.pl

You could get a little fancier and embed the tail part too:

#! /usr/bin/perl -p

BEGIN {
  die "Usage: $0 [ nagios-log ]\n" if @ARGV > 1;
  my $log = @ARGV ? shift : "/var/log/nagios/nagios.log";
  @ARGV = ("tail -f '$log' |");
}

s/(\d+)/localtime($1)/e

This works because the code written for you by -p uses Perl's "magic" (2-argument) open that processes pipes specially.

With no arguments, it transforms nagios.log, but you can also specify a different log file, e.g.,

$ ~/bin/nagiostime.pl /tmp/other-nagios.log