Use the 'e' modifier for s/// 
use warnings;
use strict;

while (<DATA>) {
    s/(Z=)(\d+)/$1 . $2*4/eg;
    my $i = 1;
    s/\b(XP)\b/$1 . ' (' . $i++ . ')'/eg;
    print;
}

__DATA__
Z=1 Z=2
Z=3
foo XP bar XP boo

[download]

Outputs: 

Z=4 Z=8
Z=12
foo XP (1) bar XP (2) boo

[download]

In reply to Re: How to find a number and replace it with calculated value? by toolic
in thread How to find a number and replace it with calculated value? by Lejocode

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