searching within a file using bash

matt007 · 07-22-2009, 09:32 AM

i get the desired result with

find . -name "*" | xargs grep -i "*searchPattern*"

---but not with

find . -name "*" | grep -i "*searchPattern*"

why this difference?

Thanks.

David the H. · 07-22-2009, 09:57 AM

Assuming I'm not mistaken, in the first pattern, find sends a list of filenames to xargs, which then runs the grep command on the files listed. In the second one, find sends the list of filenames straight into grep as a text string. You're not searching inside the files themselves, only through the list.

jlinkels · 07-22-2009, 06:09 PM

David is correct, but the correct use is:

Code:

find . -name "*" -exec grep -H searchpattern {} \;

jlinkels

David the H. · 07-23-2009, 07:52 AM

Actually, neither one is really "wrong". The "find | xargs" version is generally more efficient though, because "-exec" executes the command separately for each file, while xargs batches the jobs up into a single process.

On the other hand, xargs often has trouble handling filenames with spaces in them, so -exec may be better in that situation.

On the gripping hand, I discovered just yesterday that modern versions of find can use -exec in an xargs-like fashion. You just have to change the final semi-colon to a plus-sign.

Code:

find . -name "*" -exec grep -H searchpattern {} \+

matt007 · 07-23-2009, 08:36 AM

thanks for the info.

But i was thinking how could one really tell that with

find . -name "*" | grep -i "*searchPattern*"

we are just passing in the file names as a text string to grep...is that a property of the find command that in this case returns a "text string", is there any way to run the command so as to be able to tell that....

thanks much.

colucix · 07-23-2009, 09:30 AM

Quote:

Originally Posted by matt007

thanks for the info.

But i was thinking how could one really tell that with

find . -name "*" | grep -i "*searchPattern*"

we are just passing in the file names as a text string to grep...is that a property of the find command that in this case returns a "text string", is there any way to run the command so as to be able to tell that....

thanks much.

The find command returns a multiline string which represent the names of the files that match the search criteria:

Code:

$ find . -type f
./testfile_0
./test2
./test3
./testfile_1
./test1
./test4

if you pipe this text to the grep command, you will search a pattern inside this text as you see it on the terminal. It is the same as:

Code:

echo "./testfile_0 ./test2 ./test3 ./testfile_1 ./test1 ./test4" | grep -i "*searchPattern*"

On the contrary if you pipe this text to xargs, it uses the text (that is the list of files in this case) as argument to the specified command (grep). It equals to execute:

Code:

grep -i "*searchPattern*" ./testfile_0 ./test2 ./test3 ./testfile_1 ./test1 ./test4

jlinkels · 07-23-2009, 09:35 AM

Quote:

Originally Posted by David the H.

Actually, neither one is really "wrong". The "find | xargs" version is generally more efficient though, because "-exec" executes the command separately for each file, while xargs batches the jobs up into a single process.

I didn't say it was wrong. But showing what the "correct" use of find -exec is, might be pedantic. I could have used a better wording like "usual", or "proposed".

Quote:

Originally Posted by David the H.

Code:

find . -name "*" -exec grep -H searchpattern {} \+

It's Linux, so it is powerful, cryptic, regularly updated and hard to find.

But a good suggestion.

Quote:

Originally Posted by matt007

But i was thinking how could one really tell that with
find . -name "*" | grep -i "*searchPattern*"
we are just passing in the file names as a text string to grep...

Yes, that is what the output is of find. When piping it into xargs it is processed by xargs in such a way that the file names in that string are processed. That is how xargs behaves, but it doesn't change anything to find

jlinkels