Interpolate $1 in: s{...}{$to}

perl5ever has asked for the wisdom of the Perl Monks concerning the following question:

Consider this function:

sub foo {
  my ($text, $to) = @_;
  $text =~ s{(\d+)}{$to};
  $text;
}

print foo("123", 'capture 1 is $1');
[download]

I'd like it to print 'capture 1 is 123', but it prints 'capture 1 is $1'. It's treating $to as a string literal and ignoring the occurrence of $1 in the string.

I have since figured out this:

sub bar {
  my ($text, $to) = @_;
  $text =~ s{(\d+)}{qq{qq{$to}}}ee;
  $text;
}

print bar("456", 'capture 1 is $1'); # prints capture 1 is 456
[download]

Is there any other way to get $1, $2, etc. interpolated without resorting to using the /ee modifier?

Comment on Interpolate $1 in: s{...}{$to} Select or Download Code

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Re: Interpolate $1 in: s{...}{$to} by ikegami (Patriarch) on Jun 24, 2010 at 22:06 UTC
`'capture 1 is $1'` is a template. You need something to process that template. If you want to keep the current template format, you could use `/ee` aka `eval EXPR` (which has safety issues) or String::Interpolate (which has an unconventional interface), or you could switch to something designed to be a template (e.g. Template::Toolkit).	[reply] [d/l] [select]
Re: Interpolate $1 in: s{...}{$to} by MidLifeXis (Monsignor) on Jun 25, 2010 at 13:02 UTC
or use sprintf. Search for "format parameter index" if you need to rearrange or repeat the ordering of the matches in the output. `sub foo { my ($from, $to) = @_; return sprintf($to, ($from =~ /.../)); }` [download] --MidLifeXis	[reply] [d/l]