In addition to using an anchored(!) regex — but otherwise much as you wrote; you can also use the tr operator, like this: 
    length $h && $h !~ tr/0-9A-Fa-f//c;

[download]
This tests if $h doesn't contain any characters it shouldn't contain, and additionally, if there are any characters at all.

In reply to Re: Validating Hex Numbers by bart
in thread Validating Hex Numbers by HiFoo

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