Shouldn't that regex also match upper-case letters? Your regex will say that the string "A32g" is bad, but according to the problem description, the original poster wanted to match *any* letters, including (presumably) upper-case. So that string should match. So I would think you could just change that code to: 
if ($string =~ m!(^[A-Za-z0-9]{4})$!) {
    $string =~ tr/[a-z]/[A-Z]/;
    # or $string = uc $string;

    # do something
} else  {
    # do some error
}

[download]
I did a bit of benchmarking of uc vs. tr, and the results were pretty similar: 
Benchmark: timing 1000000 iterations of tr, uc...
        tr: 10 secs ( 7.49 usr  0.00 sys =  7.49 cpu)
        uc:  9 secs ( 6.60 usr  0.00 sys =  6.60 cpu)

[download]
So they should be pretty much interchangeable, in terms of performance.

In reply to Re: String validation by btrott
in thread String validation by Speedfreak

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