On Sun, Oct 11, 2015 at 9:34 PM, Paul Eggert <egg...@cs.ucla.edu> wrote: > greg boyd wrote: >> >> test case (single line) >> abchelloabc >> >> grep does not find the line with grep -e '^hello' nor with grep -e >> 'hello$' >> however, the line is output with >> grep -e '^hello' -e 'hello$' > > > Oooo, that's a good one. Give your student extra credit! As it happens, > the bug was recently fixed by this patch by Norihiro Tanaka: > > http://git.savannah.gnu.org/cgit/grep.git/commit/?id=256a4b494fe1c48083ba73b4f62607234e4fefd5 > > and the fix should appear in the next grep release. However, since the > patch was supposed to affect only performance, it appears that the bug fix > was due to luck, and I'm taking the liberty of adding your student's test > case by installing the attached further patch, to help prevent this bug from > coming back in a future version.
Thanks for adding that test, Paul. However, note that the bug does not require two uses of "-e" per-se. Multiple "-e"-specified regexps get translated internally to those regexps separated by the ERE "|" alternation/"or" operator. A smaller, perhaps more illustrative test case is to use an explicit "|": $ echo axa | grep -E '^x|x$' axa FYI, one can demonstrate that it was a problem in the DFA matcher without resorting to gdb by inserting a "()" in the ERE, since that construct cannot work in a DFA and grep resorts to using glibc's full-blown regex matcher. With that, even the afflicted versions of grep get the desired result (no match): $ echo axa | grep -E '^x()|x$'; echo $? $ 1
