Hello Monks;

I've been asked to review and refactor/optimize a large collection of perl5 scripts, and a great many that include regular expressions would appear to benefit from s///e, the eval modifier, as in s/PATTERN/CODE/e, iff I can substitute ANY regex for CODE. Programming Perl 4th, pg 254 says, to wit: "Applications of this technique are limitless", and I agree if I can generalize the use of any regular expression in CODE. However, things are not going according to plan in my perl (v5.36.1) built for darwin-2level. A very simple case in point (I have much more complex instances once I can get this basic example to work. 

my $str = 'This ia a real number, 123456.56';
say $str;

(my $res = $str) =~ s{ (\d+) }{ sprintf("%s", 4*$1) }xe; # $1*4, just 
+to show /e works

say $res;

say "\$1 = $1";
(my $adj = $1) =~ s/(\d)/3/g;  # replace each \d with '3', same reason
say $adj;

($res = $str) =~ s{ (\d+) }{ ($adj = $1) =~ s/(\d)/3/g }xe; # replace 
+'123456' with '333333', proof of concept

say $res;

[download]

This yields:

   This ia a real number, 123456.56
   This ia a real number, 493824.56
   $1 = 123456
   333333
   This ia a real number, 6.56

The resulting string after substitution should be 333333.56. There are, indeed 6 substitutions, so it looks like the boolean value of each iteration is being substituted. The fragment '($adj = $1) =~' I believe is required because $1 is immutable, and the result is the same with /ee. Any suggestions re patterns of regex expressions in the CODE part of S/PATTERN/CODE/ would be very appreciated.

Thanks Monks for your help.

In reply to regex in REPLACEMENT in s/// by perlboy_emeritus

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