if ( $a eq 'abcdefgh' or $b eq 'abcdefgh' or $c eq 'abcdefgh') {

}

##</code><code>##

if ( $a =~ /abcdefgh/ ||
     $b =~ /abcdefgh/ ||
     $c =~ /abcdefgh/ ||
     ....... ) {

}

##</code><code>##

my $USER_NAME = qr{abcdefgh}xms;

if ($a =~ $USER_NAME ||
    $b =~ $USER_NAME ||
    $c =~ $USER_NAME) {

}