xargs

laki47 · 03-09-2010, 04:28 PM

Hi,

I would like to ask the following:

1) ls -l |grep test -> this will grep every "ls -l" output line
2) ls -1 |xargs grep test -> this will grep every single file with test

3) ls -1 |xargs echo -> this will echo directory list
4) ls -1 |echo -> this does nothing!!!

My question is: how some command can recive input from "both sides" (grep can grep whole output or every single file - xargs, the same is for i.e. wc command). 4) echo does nothing (it's a single echo command)

Thank you

pixellany · 03-09-2010, 04:40 PM

echo expects literal text or the evaluation of a variable---not a data stream. xargs plugs in the output of "ls -1" as if it were the expected string.

Maybe think of it this way: A command that would normally read a file can get it's data from a pipe---eg grep, sed, more--and many others. If the command does not normally read from a file, then you need xargs.