use strict; 
use warnings; 
use 5.012; 
 
my %new_values_for = ( 
    Var1 => ['Variable1', 10], 
    Var2 => ['Variable2', 20], 
    Var3 => ['Variable3', 30], 
); 
 
open my $OUTFILE, ">", 'results.txt' 
    or die "Couldn't open results.txt: $!"; 
 
for my $line (<DATA>) {    #The DATA filehandle reads any lines after __DATA__ 
 
    if ($line =~ /(\w+) \s* = /xms) { 
        my $var_name = $1; 
 
        #Check if there is an entry in the hash for the current var name: 
        if (my $values = $new_values_for{$var_name}) { 
            my($new_var_name, $new_value) = @{$values}; 
 
            say $OUTFILE "$new_var_name = $new_value"; 
 
            delete $new_values_for{$var_name}; 
        }  
        else { #Variable found, but no new values are specified 
            print $OUTFILE $line; 
        } 
    } 
} 
 
 
for my $key (keys %new_values_for) { 
    my($var_name, $value)  = @{$new_values_for{$key}}; 
    say $OUTFILE "$var_name = $value"; 
} 
 
close $OUTFILE; 
 
 
 
__DATA__ 
Var1 = 1 
junk here 
Var2 = 2

$ cat results.txt 
 
Variable1 = 10 
Variable2 = 20 
Variable3 = 30