On 01/20/2012 11:45 AM, Vincent Lefevre wrote:
sed is inefficient on a regexp starting with "(.*":
$ time sed -n "s/\(.*49026\)/\1/p" ChangeLog
2012-01-12 23:39:18 (rev 49026, vinc17/xvii)
4.62s user 0.00s system 99% cpu 4.637 total
Compare to the equivalent:
$ time sed -n "s/^\(.*49026\)/\1/p" ChangeLog
2012-01-12 23:39:18 (rev 49026, vinc17/xvii)
0.27s user 0.00s system 99% cpu 0.278 total
Please reassign to glibc.
Note that depending on what you are trying to do, you might like these
fast alternatives that do not use grouping parentheses:
time sed -n 's/.*49026/&/p' ChangeLog
time sed -n '/.*49026/p' ChangeLog
In particular, outside the s/// command the parentheses are ignored, so
this is also fast.
time sed -n '/\(.*49026\)/p' ChangeLog
Paolo
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