Use qr//. It is used to store a regex in a variable. Think you want something like this.

my $re = qr/.+\-(.+)/;
$foo =~ s/$re/$1/;
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but if all are in domain-computer form, you could just use

$foo =~ s/.+\-(.+)/$1/;
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Update: but on second thought the first way could run in a loop and you could just define the regex before the loop using qr//. That would probably be more efficient.

Example:

use strict;
my $re = qr/.+\-(.+)/;

while(<DATA>){
    s/$re/$1/;
    print;
}

__DATA__
domain-comp1
domain-comp2
domain-comp3
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Output:

comp1
comp2
comp3
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