Re: regex Quantifiers {m,n}, m can be negative, n greater than 255

jian he <jian(dot)universality(at)gmail(dot)com> writes:
> select regexp_matches(E'abc', 'a{0,257}.');
> select regexp_matches(E'abc', 'a{-0,257}.');
> select regexp_matches(E'abc', 'a{-1,2}.');

> based on the manual description, the second and the third query should
> error out?

No. Read

https://www.postgresql.org/docs/current/functions-matching.html#POSIX-ATOMS-TABLE

which says that '{'

when followed by a character other than a digit, matches the
left-brace character {; when followed by a digit, it is the
beginning of a bound (see below)

So your second and third patterns are just literal matches, except
for the final '.'.

You can quibble about how bright that choice was, but I think it's
mandated by POSIX, not just something that Henry Spencer thought up.

regards, tom lane