Question

I have a script that outputs about 10 lines every time if it run. The content of these lines varies.

I would really like to be able to grep in the output and do different things depending on the output.

In pseudo this is what I would like to do

cat /etc/password | \\
if [ grep "root" $STDOUT ]; then
   echo "root is found"

elif [ grep "nobody" $STDOUT ]; then
   echo "nobody is found"

fi

Here have I used cat /etc/password as an example, but it should be replaced with my scripts mentioned above.

The problem is, how do I get hold of the output from cat /etc/password in the if/elif conditions?

Answer 1

As @Benoit recommends, just use grep directly.

As @larsmans notes, you can avoid a double-read of the file by reading it into a variable once.

Given the availability of bash I’d do it like this:

password=$(< /etc/passwd)

if grep -q root <<< "$password" ; then
    echo root found
elif grep -q nobody <<< "$password" ; then
    echo nobody found
fi

One read of the file, one or two invocations of grep, no other processes or subshells launched.