Run Perl 5 online — the classic scripting swiss army knife.
Perl 5 outlived every announcement of its death. Perfect regex, deep CPAN library, and script glue everywhere Linux runs. Ops teams still write it; genomics research still writes it; log-mining pipelines still write it.
ls-judge runs Perl 5 inside a Firecracker microVM.
Clicking "Run now" opens the playground with this exact code and a matching test case pre-loaded — passes on first Run.
my $n = <STDIN>;
chomp $n;
print $n * 2, "\n";
21
42