Thread: PLPGSQL regexe

I'm doing a check within a PL/PGSQL function using a regular expression
and I get the error:

ERROR:  regcomp failed with error invalid character range

This appears to be because of the underscore "_" character. The regex I
want to use is ''[A-Za-z0-9_]'' but this doesn't work. Any suggestions
or is this a bug/feature?