s/// is an operator, so that means your variable contains Perl code. eval EXPR can be used to execute it.

But that's rather unsafe. I assume you don't want to allow arbitrary code execution (variable lookups, (?{}), (??{}) and /e). If so, you can use the following: 

my ($pat, $repl, $mods) = $substitution =~ m{
    ^s/
    ( (?:[^/\\]+|\\.)* )
    /
    ( .* )
    /
    ( [a-z]* )
    \z
}xs
    or die("Bad substitution\n");

my %mods = map { $_ => 1 } $mods =~ /./sg;
my $global = delete($mods{g});
$mods = join('', delete(@mods{qw( i m s x )}))
   and $pat = "(?$mods:$pat)";

die("Unknown modifiers \"", keys(%mods), "\"\n")
    if %mods;

no re 'eval';
if ($global) {
    $candidate =~ s/$pat/$repl/g;
} else {
    $candidate =~ s/$pat/$repl/;
}

[download]

In reply to Re: Substitution with regexes in variables by ikegami
in thread Substitution with regexes in variables by nafion112

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