File: grep.info,  Node: Known Bugs,  Up: Reporting Bugs

6.1 Known Bugs
==============

Large repetition counts in the ‘{n,m}’ construct may cause ‘grep’ to use
lots of memory.  In addition, certain other obscure regular expressions
require exponential time and space, and may cause ‘grep’ to run out of
memory.

   Back-references can greatly slow down matching, as they can generate
exponentially many matching possibilities that can consume both time and
memory to explore.  Also, the POSIX specification for back-references is
at times unclear.  Furthermore, many regular expression implementations
have back-reference bugs that can cause programs to return incorrect
answers or even crash, and fixing these bugs has often been
low-priority: for example, as of 2021 the GNU C library bug database
(https://sourceware.org/bugzilla/) contained back-reference bugs 52,
10844, 11053, 24269 and 25322, with little sign of forthcoming fixes.
Luckily, back-references are rarely useful and it should be little
trouble to avoid them in practical applications.