When to use xargs when piping?

Question

I am new to bash and I am trying to understand the use of xargs, which is still not clear for me. For example:

history | grep ls

H

Answer 1

When you use piping without xargs, the actual data is fed into the next command. On the other hand, when using piping with xargs, the actual data is viewed as a parameter to the next command. To give a concrete example, say you have a folder with a.txt and b.txt. a.txt contains just a single line 'hello world!', and b.txt is just empty.

If you do

ls | grep txt

you would end up getting the output:

a.txt
b.txt

Yet, if you do

ls | xargs grep txt

you would get nothing since neither file a.txt nor b.txt contains the word txt.

If the command is

ls | xargs grep hello

you would get:

hello world!

That's because with xargs, the two filenames given by ls are passed to grep as arguments, rather than the actual content.