How do I pass a list of files to grep

Question

I am using find and getting a list of files I want to grep through. How do I pipe that list to grep?

Answer 1

Well, the generic case that works with any command that writes to stdout is to use xargs, which will let you attach any number of command-line arguments to the end of a command:

$ find … | xargs grep 'search'

Or to embed the command in your grep line with backticks or $(), which will run the command and substitute its output:

$ grep 'search' $(find …)

Note that these commands don't work if the file names contain whitespace, or certain other “weird characters” (\'" for xargs, \[*? for $(find …)).

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However, in the specific case of find the ability to execute a program on the given arguments is built-in:

$ find … -exec grep 'search' {} \;

Everything between -exec and ; is the command to execute; {} is replaced with the filename found by find. That will execute a separate grep for each file; since grep can take many filenames and search them all, you can change the ; to + to tell find to pass all the matching filenames to grep at once:

$ find … -exec grep 'search' {} \+

Answer 2

Some versions of grep (e.g. on non-embedded Linux or BSD or Mac OS X) have a -r option to make a recursive search. On OpenBSD, use -R (and there's no --exclude as in the example below). This covers simple combinations of find with grep.

If your implementation doesn't have the -R flag, or if you want fancier file matching criteria, you can use the -exec primary of find to make it execute grep. A few older find implementations don't support -exec … +; on these systems, use a ; instead of the + (this will call grep once per file, so it'll be slower, but otherwise the result will be the same). Note the /dev/null trick to cause grep to show the file name even if it happens to be called on a single file (GNU grep and FreeBSD/NetBSD/OSX grep have a -H option to achieve the same effect).

find . -type f -name '*.o' -prune -o -exec grep 'needle' /dev/null {} +
grep -r --exclude='*.o' 'needle' .