Michael Limberger

Need me? Email mike@limberger.ca

2024-06-24

This note is about Perl's eval loop pattern. It is one of those small tricks that looks odd the first time you see it, then becomes hard to put down once you need dynamic code paths.

#!/usr/bin/env perl
use feature qw|say|;

$_ = <<'EOF';
10;
s~(\\d+)(?{ say qq($1) })~$1-1~e;
sleep 1;
$1 ? eval : say q(Countdown complete!);
EOF

eval;

Match a number, print it, replace it with itself minus one, sleep, and if $1 is still true, eval the string again.