Thread

1. regex Quantifiers {m,n}, m can be negative, n greater than 255

   jian he <jian.universality@gmail.com> — 2025-12-11T12:56:03Z

   hi.
   
   ""
   The forms using {...} are known as bounds. The numbers m and n within a bound
   are unsigned decimal integers with permissible values from 0 to 255 inclusive.
   ""
   Table (Regular Expression Quantifiers)
   https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-POSIX-REGEXP
   
   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?
   test_regex.sql (begin with line 223) have many tests but no tests for
   negative value.
   
   
   
   --
   jian
   https://www.enterprisedb.com
   
   
   
   

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

   Tom Lane <tgl@sss.pgh.pa.us> — 2025-12-11T15:46:54Z

   jian he <jian.universality@gmail.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