With find
:
cd /the/dir
find . -type f -exec grep pattern {} +
(-type f
is to only search in regular files (also excluding symlinks even if they point to regular files). If you want to search in any type of file except directories (but beware there are some types of files like fifos or /dev/zero that you generally don't want to read), replace -type f
with the GNU-specific ! -xtype d
(-xtype d
matches for files of type directory after symlink resolution)).
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). Non-regular files won't be searched unless you add a -D read
option. Recent versions of GNU grep
will still not search inside symlinks though.
Very old versions of GNU find
did not support the standard {} +
syntax, but there you could use the non-standard:
cd /the/dir &&
find . -type f -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 . -type f -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 . -type f -print0 | stdbuf -oL xargs -n1000 -r0P3 grep pattern
(on a recent GNU or FreeBSD system) or use the --line-buffered
option of GNU grep
.
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.
Since the exit status of grep
indicates whether or not it found a match, you should be able to test that directly as a find
predicate (with the necessary negation, !
or -not
) e.g.
find . -type f -name "*.c" \( -exec grep -q "ABC" {} \; ! -exec grep -q "123" {} \; \) -print
-q
makes grep
exit silently on the first match - we don't need to hear from it because we let find
print the filename.
Best Answer
grep
returns a different exit code if it found something (zero) vs. if it hasn't found anything (non-zero). In anif
statement, a zero exit code is mapped to "true" and a non-zero exit code is mapped to false. In addition, grep has a-q
argument to not output the matched text (but only return the exit status code)So, you can use grep like this:
As a quick note, when you do something like
if [ -z "$var" ]…
, it turns out that[
is actually a command you're running, just like grep. On my system, it's/usr/bin/[
. (Well, technically, your shell probably has it built-in, but that's an optimization. It behaves as if it were a command). It works the same way,[
returns a zero exit code for true, a non-zero exit code for false. (test
is the same thing as[
, except for the closing]
)