Interpolate into replacement with s//?

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

I need to pass in from a config file, a regexp and replacement for s// but can't seem to work out how to allow $1, $2 in the replacement:

$string = 'ABC';
$search = qr/^(A)/;
$replace = '$1Z';
$string = s/$search/$replace/g;
say $string;
[download]

I would like to see "AZBC", for example but the $1 is interpreted as literal, as I suppose I should expect. Is there some way to have the replacement interpret $1, $2 etc?

Comment on Interpolate into replacement with s//? Download Code

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Re^2: Interpolate into replacement with s//? by ikegami (Patriarch) on Nov 09, 2011 at 20:43 UTC
`$replace` contains a template. Therefore, you need a template engine to process it. The only existing template module I know that can process that language is String::Interpolate. (Yeah, it has a weird interface.) Alternatively, if `$replace` actually contained a string literal (i.e. Perl code), you could use `eval` to evaluate it. `$string = 'ABC'; $search = qr/^(A)/; $replace = '"$1Z"'; $string = s{$search}{ my $replacement = eval($replace); die $@ if $@; $replacement }eg; say $string;` [download]	[reply] [d/l] [select]
Re^3: Interpolate into replacement with s//? by tchrist (Pilgrim) on Nov 09, 2011 at 20:54 UTC
ikegami wrote: `$replace` contains a template. Therefore, you need a template engine to process it. Aw `/gee` whiz, we don’t need no stinkin’ modules for such a trivial task. Merely render unto Perl that which is Perl’s: `use v5.14; my $string = q/ABC/; my $search = qr/^(A)/; my $replace = q/"Z\l$1Z"/; $string =~ s/$search/$replace/gee; say $string;` [download] Which when run duly prints out `ZaZBC`.	[reply] [d/l]
Re^4: Interpolate into replacement with s//? by philkime (Beadle) on Nov 09, 2011 at 21:18 UTC
Hmm, I tried /gee but $replace isn't directly assigned, it's from elsewhere so say I'd read $replace from another file and it was a string 'Z$1Z' then this doesn't seem to work?	[reply]
Re^5: Interpolate into replacement with s//? by ikegami (Patriarch) on Nov 09, 2011 at 21:31 UTC
Re^6: Interpolate into replacement with s//? by philkime (Beadle) on Nov 10, 2011 at 09:14 UTC
Some notes below your chosen depth have not been shown here
Re: Interpolate into replacement with s//? by SuicideJunkie (Vicar) on Nov 09, 2011 at 20:40 UTC
It was a little hard to find, but this may be what you want: perlretut Says: A modifier available specifically to search and replace is the s///e evaluation modifier. s///e treats the replacement text as Perl code, rather than a double-quoted string. The value that the code returns is substituted for the matched substring. s///e is useful if you need to do a bit of computation in the process of replacing text. This example counts character frequencies in a line:	[reply]