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I have directory with cca 26 000 files and I need to grep in all these files. Problem is, that I need it as fast as possible, so it's not ideal to make script where grep will take name of one file from find command and write matches to file. Before "arguments list too long" issue it took cca 2 minutes to grep in all this files. Any ideas how to do it? edit: there is a script that is making new files all the time, so it's not possible to put all files to different dirs.

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use find with xargs or grep -R –  Eddy_Em Aug 7 '13 at 8:37
    
It works good, but it takes 10 minutes... –  user2778979 Aug 7 '13 at 9:18

3 Answers 3

up vote 1 down vote accepted

With find:

cd /the/dir
find . -exec grep pattern {} +

With GNU grep:

grep -r pattern /the/dir

(but beware that unless you have a recent version of GNU grep, that will follow symlinks when descending into directories).

Very old versions of GNU find did not support the standard {} + syntax, but there you could use the non-standard:

cd /the/dir
find . -print0 | xargs -r0 grep pattern

Performances are likely to be I/O bound. That is the time to do the search would be the time needed to read all that data from storage.

If the data is on a redundant disk array, reading several files at a time might improve performance (and could degrade them otherwise). If the performances are not I/O bound (because for instance all the data is in cache), and you have multiple CPUs, concurrent greps might help as well. You can do that with GNU xargs's -P option.

For instance, if the data is on a RAID1 array with 3 drives, or if the data is in cache and you have 3 CPUs whose time to spare:

cd /the/dir
find . -print0 | xargs -n1000 -r0P3 grep pattern

(here using -n1000 to spawn a new grep every 1000 files, up to 3 running in parallel at a time).

However note that if the output of grep is redirected, you'll end up with badly interleaved output from the 3 grep processes, in which case you may want to run it as:

find . -print0 | stdbuf -oL xargs -n1000 -r0P3 grep pattern

(on a recent GNU or FreeBSD system)

If pattern is a fixed string, adding the -F option could improve matters.

If it's not multi-byte character data, or if for the matching of that pattern, it doesn't matter whether the data is multi-byte character or not, then:

cd /the/dir
LC_ALL=C grep -r pattern .

could improve performance significantly.

If you end up doing such searches often, then you may want to index your data using one of the many search engines out there.

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Thanks, second sugestion works just fine. btw: do you know about possibility that will allow me to grep even faster? –  user2778979 Aug 7 '13 at 9:27

26000 files in a single directory is a lot for most filesystems. It's likely that a significant part of the time is taken reading this big directory. Consider splitting it into smaller directories with only a few hundred files each.

Calling find cannot explain poor performance unless you do it wrong. It's a fast way of traversing a directory, and of ensuring that you don't risk attempting to execute a command line that's too long. Make sure that you use -exec grep PATTERN {} +, which packs as many files as it can per command invocation, and not -exec grep PATTERN {} \;, which executes grep once per file: executing the command once per file is likely to be significantly slower.

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Thanks, I will google something about it and probably I will split that. I made exactly what you are writing about and it took 3 times longer than only grep... –  user2778979 Aug 9 '13 at 11:53

All files in the directory

grep 'search string' *

with recursively

grep -R 'search string' *
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Care to elaborate the -1? –  Markus Aug 7 '13 at 9:31
3  
I didn't downvote, but there are a few issues with yours: the OP mentionned a "arg list too long", which your first one won't fix and is probably what the OP was doing before. The second one doesn't help either in that regard (would have helped had you used . instead of *). * will exclude dot files (though with -R, not the ones in the recursed directories). -R as opposed to -r follows symlinks even with recent versions of GNU grep. You'll also have an issue with files in the current directory whose name starts with - –  Stéphane Chazelas Aug 7 '13 at 11:20

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