Hello, Backreferences don't work with -w or -x in combination with -P:
$ echo aa | grep -Pw '(.)\1' $ Or they work in an unexpected way: $ echo aa | grep -Pw '(.)\2' aa The fix is simple: --- src/pcresearch.c~ 2014-02-24 09:59:56.864374362 +0000 +++ src/pcresearch.c 2014-02-24 07:33:04.666398105 +0000 @@ -75,9 +75,9 @@ Pcompile (char const *pattern, size_t si *n = '\0'; if (match_lines) - strcpy (n, "^("); + strcpy (n, "^(?:"); if (match_words) - strcpy (n, "\\b("); + strcpy (n, "\\b(?:"); n += strlen (n); /* The PCRE interface doesn't allow NUL bytes in the pattern, so