Bash - issue with grep conditional statement

Question

Why does this code work correctly, while the other version of the same condition doesn't?

if grep -q string file; then
    echo found
else
    echo not found
fi

This doesn't work:

if [ ! `grep -q string file` ]; then
    echo not found
else
    echo found
fi

Why have you changed the syntax on the two examples?, just a ! to your original example — Raman Sailopal, Oct 20 '17 at 09:04
Do you know what -q does, or are you just blindly using it because you've seen others use it? — chepner, Oct 21 '17 at 01:27

Kusalananda · Accepted Answer · 2017-10-20T11:07:33.563

6

`grep -q string file`, in backticks (or inside $(...), which is preferable), will be replaced by the output of grep. This will be an empty string since -q is used.

To negate a test, just insert ! before it:

if ! grep -q pattern file; then
    echo not found
else
    echo found
fi

If you truly want to search for a string (rather than a regular expression), then you should use -F with grep as well.

edited Oct 20 '17 at 11:07

answered Oct 20 '17 at 09:19

Kusalananda

333,661

Bash - issue with grep conditional statement

1 Answers1