Very similar to a recent question. See Re: Trying to compare a string....

Update: In your case, regular expression would be the easiest solution: 

my $dna = shift; # Get the first command line argument.
if ($dna =~ /[^ACTG]/g) {
    die "Non-nucleotide at " . pos($dna);
}

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: If/else within a foreach loop to check strings within an array by choroba
in thread If/else within a foreach loop to check strings within an array by Anonymous Monk

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