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if ($string =~ /[^A-Z0-9]/) { # String contains a character other than A-Z, 0-9. ... # String only contains characters A-Z, 0-9. ... }
if ($string =~ /^[A-Z0-9]*\z/) { # String only contains characters A-Z, 0-9. ... # String contains a character other than A-Z, 0-9. ... }