in reply to Regular expression "replace string interpolation" problem

This should work: 
...
my $replace = '"$1 Perl"';

$text2 =~ s/$match/$replace/ee;

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Or you might want to write it like this: 
my $replace = '$1 Perl'; # use original setting of $replace

$text2 =~ s/$match/'"'.$replace.'"'/ee;

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Probably even a better solution would be write $replace as a subroutine: 

my $replace = sub { "$1 Perl" };

$text2 =~ s/$match/$replace->()/e;

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and then only level of evaluation is needed.

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Re^2: Regular expression "replace string interpolation" problem
by cLive ;-) (Prior) on May 16, 2008 at 22:25 UTC

    That works - thanks :)

    But, reading through the regex documentation, I still can't work out exactly why. Hmmm.

    so I guess needs to be \\" in the replace string for quotes. Arghhh, double escaping!!

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      Or how to embed " in the output - but that's not a biggie right now.

      You want to produce the code 
      "$1 \"Perl\""

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      so 
      my $replace = '"$1 \\"Perl\\""';  # Produces: "$1 \"Perl\""
s/$match/eval $replace/e

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      Technically, the slashes don't need to be doubled since single quotes are forgiving when it's unambiguous.

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      To explain what's going on it might be helpful to use underlined bold text to represent strings. So, one can write:
      eval 2+2 → 4
      and this means if you eval the string 2+2, you'll get the string 4. In perl this is just: 
      my $x = '2+2';
my $y = eval $x; # $y is the string '4'

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      In your original example, what is happening during the substitution s/$match/$replace/e is:

      eval $replace → $1 Perl
      I.e., the match is replaced with the string $1 Perl, and that is why $text2 contains $1 Perl world.

      How about just adding another /e modifier to evaluate the substitution again? Unfortunately this doesn't work because $1 Perl world is not valid perl syntax:

      eval eval $replace → eval $1 Perl world → syntax error

      When $replace and the substitution is written as: 

      my $replace = '"$1 Perl"';
$text2 =~ s/$match/$replace/ee;

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      the evaluation of the replacement proceeds as follows:
      eval eval $replace → eval "$1 Perl"
      and because of the double quotes this last eval yields $1 concatenated with a space and the string Perl.
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