I have a regex search expression, and then a replacement expression.
My requirement is to have function call invocations embedded in the replacement expression that would be kept separate from the logic - say at the beginning of the script, and I want the replacement expression to be evaluated when the search and replacement is done - and not when the replacement expression is initialized to the variable that contains it.

And now some code of (what I want to do in comments) what I have:

use strict;
use warnings;

use Data::Dumper;

use Tie::File;

# open the file if it exists, but fail if it does not
use Fcntl 'O_RDWR';

our @array = ();

our $file = 'taste';

tie @array, 'Tie::File', $file, mode => O_RDWR or die $!;

our $SearchString = 'HAI WORLD Times ([0-9]+).*$';
#our $ReplaceString = "\t\t<exML LOLZ = \"" . unpack('a1', $1) . '"/>'
+; # we could use such a statement ONLY if we figured out what somethi
+ng() would be

my $elementIdx = 0;

while($elementIdx <= $#array)
{
    if($array[$elementIdx] =~ $SearchString)
    {
        # Maintain only the first character
        
        #$array[$elementIdx] = unpack ('a' . (1 + length("\t\t<exML LO
+LZ = \"\"/>")), something($ReplaceString)); # I would love to know wh
+at something() could be so that I can separate the configuration from
+ the logic  
        $array[$elementIdx++] = "\t\t<exML LOLZ = \"" . unpack('a1', $
+1) . '"/>';
        #++$elementIdx;
    }
    else
    {
        splice @array, $elementIdx, 1;
        # we don't want this in the output
    }
}

untie @array;    # all done!
[download]

Sample input file:

HAI WORLD Times 0
HAI WORLD Times 1
HAI WORLD Times 2
HAI WORLD Times 3
HAI WORLD Times 4
HAI WORLD Times 5
HAI WORLD Times 6
HAI WORLD Times 7
HAI WORLD Times 8
HAI WORLD Times 9
HAI WORLD Times 10
HAI WORLD Times 11
HAI WORLD Times 12
HAI WORLD Times 13
HAI WORLD Times 14
HAI WORLD Times 15
HAI WORLD Times 16
HAI WORLD Times 17
HAI WORLD Times 18
HAI WORLD Times 19
HAI WORLD Times 20
HAI WORLD Times 21
HAI WORLD Times 22
HAI WORLD Times 23
HAI WORLD Times 24
HAI WORLD Times 25
[download]

Corresponding output file:

        <exML LOLZ = "0"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "2"/>
        <exML LOLZ = "3"/>
        <exML LOLZ = "4"/>
        <exML LOLZ = "5"/>
        <exML LOLZ = "6"/>
        <exML LOLZ = "7"/>
        <exML LOLZ = "8"/>
        <exML LOLZ = "9"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "1"/>
        <exML LOLZ = "2"/>
        <exML LOLZ = "2"/>
        <exML LOLZ = "2"/>
        <exML LOLZ = "2"/>
        <exML LOLZ = "2"/>
        <exML LOLZ = "2"/>
[download]

What would something() look like?
Update : Unfortunately, something looks like eval... oh well...

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