first, a character class might contain a variable with as few as one character in it (/[$foo]/);

... and in that case, it's worthwhile to test the variable first, to make sure it contains something (i.e. length($foo)>0), because an empty string in that position is a runtime error, if I'm not mistaken.

In reply to Re^2: Why would one want in a regex a class with only a single entry? by graff
in thread Why would one want in a regex a class with only a single entry? by ack

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