in reply to how do I use s///e

call a subroutine from there. This is very usefull whenever the replacement is not the same on each iteration.
Boris

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Re: Re: how do I use s///e
by perlfan (Parson) on Jan 26, 2004 at 18:52 UTC
    Agreed. Combining the ability to call a subroute to do your bidding and back references makes for some very handy abilities.
    For example:
    Say I have a string:

    "The %NOUN% can jump very %ADVERB%"

    And say I have hash: 
    %wordBank = (
NOUN => "kangaroo",
ADVERB => "far",
)

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    I wanted to replace what is in the string with what is in the hash, so originally, I iterated through the hash and did a replace on the string as I found each hash key. This is terribly inefficient, so I reworked it to find items delimited by %..% in the string, and used the delimited keyword to directly call the value from the hash. This save me a lot of time, especially when %wordBank is very large. 
    #!/usr/bin/perl -w
  use strict;
  sub safeReplace {
    my($hashkey,%hash) = @_;
    my $hash = \%hash;  
    my $retval = '';
    if (defined($hash{$hashkey})) {
      $retval = $hash{$hashkey};
    }  else {
      $retval = "\%$hashkey\%";
    }
    return $retval;
  }

  sub preProcessStr {
    my($string,%options) = @_;
    $string =~ s/%(.+?)%/safeReplace($1,%options)/ge;
    return $string;
  }
  
  my  %options = (
              ARG1 => "test",
              ARG2 => "123...",
             );
  my $string = 'Hello %ARG1%, counting down %ARG2% .. %NOT%';
  
  $string = preProcessStr($string,%options);
  print "$string\n"

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      I realize your code was mainly for demonstration purposes, but it can be shortened considerably. I'm sure this can be golfed down even more, but I came up with the following snippet, which I feel is simple yet not too obfuscated (and also demonstrates the use of s///e, so I guess it's not really too OT):

      #!/usr/bin/perl
use strict;
use warnings;

my $str = 'The %NOUN% can jump very %ADVERB% with his %APPENDAGES%';

my %wb = (
    NOUN   => "kangaroo",
    ADVERB => "far",
);

$str =~ s/%([^%]+)%/$wb{$1} || "\%$1\%"/ge;

print "$str\n";

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      Update: %s/\$template/\$str/g; silly mistake caused by last-minute-edits-without-testing. Thanks to Not_a_Number for the catch.

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        Thanks :)
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