use Modern::Perl qw/2015/;

my @regex = <DATA>;
chomp @regex;
my $regex = join '|', @regex;
$regex = qr/$regex/;

open( my $FH, '<', 'data.txt' ) or die "Could not open file: $!";
while ( my $line = <$FH> ) {
    print "Matched $1 at $line" if $line =~ m/^($regex)/;
}

__DATA__
GSAD1234
GSAD2345
GSAD4567