Question

I have a file which contains filenames (and the full path to them) and I want to search for a word within all of them. some pseudo-code to explain:

grep keyword <all files specified in files.txt> 

or

cat files.txt > grep keyword cat files txt | grep keyword 

the problem is that I can only get grep to search the filenames, not the contents of the actual files.

Answer 1

cat files.txt | xargs grep keyword 

or

grep keyword `cat files.txt` 

or (equivalent to previous but harder to mis-read)

grep keyword $(cat files.txt) 

should do the trick.

Pitfalls:

• If files.txt contains file names with spaces, either solution will malfunction, because ‘This is a filename.txt’ will be interpreted as four files, ‘This’, ‘is’, ‘a’, and ‘filename.txt’. A good reason why you shouldn’t have spaces in your filenames, ever.

  • There are ways around this, but none of them is trivial. (find … -print0 / xargs -0 is one of them.)

• The second (cat) version can result in a very long command line (which might fail when exceeding the limits of your environment). The first (xargs) version handles long input automatically; xargs offers several options to control the details.