Question

So I’m trying to use the sh (Bourne Shell) to write some scripts. I keep running into this confusion. For the following:

1. rm `echo test`
2. echo test | rm

I know backticks are used to run the command first, okay.
But for piping in #2, why doesn’t rm take in test as an argument? Is there something about piping I don’t understand? I thought it was simply sending output of one command as the input to another.

And… related to my piping confusion maybe.

dir=/blah/blar/blar
files=`ls ${dir} -rt`
count=`wc -l $files` # doesn't work, in fact it's running it along with each file that exists
count2=`$files | wc -l` # doesn't work

How come I can’t store the ls into “files” and use that?

Answer 1

You would need to use xargs there, as rm takes arguments to delete, it doesn’t read from the STDIN (which is what pipes typically pipe).

echo test | xargs rm

The first one works because backticks are for substitutions, much like ${} but not as easy. 🙂

Alternatively, you could use find.

find . -name test -exec rm -f '{}' \;