What is the difference between cat source.txt | grep x and grep x source.txt?

Question

I saw an example where some one did this:

cat source.txt | grep a

But I always do it like:

grep a source.txt

What's the difference between the two?

Not a great deal. `grep` (like many standard *nix utils) can process either stdin or files named as command-line args. — Oliver Charlesworth, Aug 18 '14 at 20:52
One of them [annoys old-fashioned Unix users](http://en.wikipedia.org/wiki/Cat_(Unix)#Useless_use_of_cat)... ("Useless use of cat" or UUOC) — Michael Berkowski, Aug 18 '14 at 20:57
@OliCharlesworth What is the pipe symbol used for in general? — user2030677, Aug 18 '14 at 21:30

score 1 · Accepted Answer · answered Aug 18 '14 at 20:58

1

The first one is a classical “useless use of cat” (UUOC).

answered Aug 18 '14 at 20:58

lxg

1 Answers1