Back substitution expansion

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

my $s = "foo bar quux";
my $pattern = q(foo (.*?) quux);
my $rep = q(foo quux $1);
$s =~ s|$pattern|$rep}|;
print "$s\n";

I would like for this to print

foo quux bar

But instead I get

foo quux $1

How can I get the substitution operator to expand the $1 embedded in the replacement variable?

Comment on Back substitution expansion

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Re: Back substitution expansion by japhy (Canon) on Aug 20, 2001 at 03:52 UTC
You'll need to go through a bit of effort: `s/$pattern/qq[qq[$rep]]/ee;` [download] _____________________________________________________ Jeff`[japhy]`Pinyan: Perl, regex, and perl hacker. `s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;`	[reply] [d/l]
Re: Back substitution expansion by Monky Python (Scribe) on Aug 20, 2001 at 11:15 UTC
japhy already found the solution.. The perlop manpage tells you a little more about the /e option: A /e will cause the replacement portion to be treated as a full-fledged Perl expression and evaluated right then and there. It is, however, syntax checked at compile-time. A second e modifier will cause the replacement portion to be evaled before being run as a Perl expression. MP	[reply]