11–20 of 47 posts
When running 'look' to get all comments in a file I only get the first found line in the ouput. Can someone explain this? look "#" .zshrc There are really a lot more comments (lines starting with '#') in my .zshrc then the first line.
When running 'look' to get all comments in a file I only get the first found line in the ouput. Can someone explain this? look "#" .zshrc There are really a lot more comments (lines starting with '#') in my .zshrc then the first line.
> As look performs a binary search, the lines in file must be sorted...
I assume you didn't sort your source file first.
look uses a linear search by default instead of a binary search, which is what most other implementations use by default.
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I created a 1.1G file with dictionary words and timed... % du -h a 1.1G a % time look 'dog' a | wc -l 53856 real 0m0.021s user 0m0.020s sys 0m0.003s % time grep '^dog' a | wc -l 53856 real 0m28.593s user 0m0.977s sys 0m2.223s Ok grep performed worse than what I expected (sort took a long time though).
Is grep optimized to be fast, though? There seems to be a lot of, "better at grep than grep" tools out there, http://beyondgrep.com/
When running 'look' to get all comments in a file I only get the first found line in the ouput. Can someone explain this? look "#" .zshrc There are really a lot more comments (lines starting with '#') in my .zshrc then the first line.
From the manpage: > As look performs a binary search, the lines in file must be sorted... I assume you didn't sort your source file first.
sort ~/.zshrc -o /tmp/.zshrc
look "#" /tmp/.zshrc
Sorry for the noise but I am confused... :|
Earlier quoted context omitted.
I created a 1.1G file with dictionary words and timed... % du -h a 1.1G a % time look 'dog' a | wc -l 53856 real 0m0.021s user 0m0.020s sys 0m0.003s % time grep '^dog' a | wc -l 53856 real 0m28.593s user 0m0.977s sys 0m2.223s Ok grep performed worse than what I expected (sort took a long time though).
Is grep optimized to be fast, though? There seems to be a lot of, "better at grep than grep" tools out there, http://beyondgrep.com/
As for grep itself, it has had many incarnations over the decades with various pluses and minuses.
The current GNU grep allows 3 kinds of regex, basic/extended/perl -- the latter being what ack supports.
Note that Perl regexes have extensions beyond regular languages that are inherently slower than the automata specified by basic regexes. Power versus speed.
E.g. grep(1): "Back-references are very slow, and may require exponential time."
For further info:
> why GNU grep is fast > Mike Haertel mike at ducky.net > Sat Aug 21 03:00:30 UTC 2010
> Here's a blog post from 2006 about a developer trying to "beat grep" and looking at the algorithms it uses; it goes into a little more detail about the "doesn't need to do the loop exit test at every step" optimization mentioned in this email.
http://ridiculousfish.com/blog/posts/old-age-and-treachery.h...
via
https://lists.freebsd.org/pipermail/freebsd-current/2010-Aug...
The best writeup is surely by the inimitable Russ Cox, who really really explains clearly when grep as of 2007 was one of the only fast regex implementations:
Regular Expression Matching Can Be Simple And Fast [#1] (but is slow in Java, Perl, PHP, Python, Ruby, ...)
Russ Cox 2007 jan
http://swtch.com/~rsc/regexp/regexp1.html
(This is a 4 part series but IIRC part 1 has the highlights)
I'm sure that various other tools have been strongly influenced by this famous essay, and so many more things may be as fast as grep by now, but still...
P.S. one of the other high profile "ack"-like search tools would be "ag", aka "The Silver Surfer".
"The Silver Searcher is a 3-5x faster drop in replacement for ack (which itself is better than grep)."
2013
https://www.reddit.com/r/programming/comments/16bvah/the_sil...
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Some others I like: rev, vipe, comm, bfr, xxd
Do you know of a good resource listing all of these?
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From the manpage: > As look performs a binary search, the lines in file must be sorted... I assume you didn't sort your source file first.
When sorting the file first I get no output anymore: sort ~/.zshrc -o /tmp/.zshrc look "#" /tmp/.zshrc Sorry for the noise but I am confused... :|
Earlier quoted context omitted.
From the manpage: > As look performs a binary search, the lines in file must be sorted... I assume you didn't sort your source file first.
When sorting the file first I get no output anymore: sort ~/.zshrc -o /tmp/.zshrc look "#" /tmp/.zshrc Sorry for the noise but I am confused... :|
Try setting LC_COLLATE=C and export it and retry.