Grepping a list of words
swell.k at gmail.com
Thu Aug 12 17:09:52 UTC 2010
Oliver Fromme <olli at lurza.secnetix.de> writes:
> John Levine <johnl at iecc.com> wrote:
> > > > % egrep 'word1|word2|word3|...|wordn' filename.txt
> > > Thanks for the replies. This suggestion won't do the job as the list of
> > > words is very long, maybe 50-60. This is why I asked how to place them all
> > > in a file. One reply dealt with using a file with egrep. I'll try that.
> > Gee, 50 words, that's about a 300 character pattern, that's not a problem
> > for any shell or version of grep I know.
> > But reading the words from a file is equivalent and as you note most
> > likely easier to do.
> The question is what is more efficient. This might be
> important if that kind of grep command is run very often
> by a script, or if it's run on very large files.
> My guess is that one large regular expression is more
> efficient than many small ones. But I haven't done real
> benchmarks to prove this.
BTW, not using regular expressions is even more efficient, e.g.
$ fgrep -f /usr/share/dict/words /etc/group
When using egrep(1) it takes considerably more time and memory.
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