-n option with grep command

Shell Programming and Scripting
1

Hi,

what is the meaning of -n option before the grep command ?

grep command searches for the specified string in the file tmp_crontab.txt

but what does -n mean ?

[ -n "`grep $some_string /tmp/tmp_crontab.txt`" ]

With Regards

2

Nothing with grep but with string :
[ -n "String" ] returns TRUE if string is not empty.

likely [ -z "String" ] returns TRUE if string is empty.

"`grep $some_string /tmp/tmp_crontab.txt`" is a command substitution returning a string value. It can be better written "$(grep $some_string /tmp/tmp_crontab.txt)"

Example ($> stands for the prompt):

$> grep root /etc/passwd
root:x:0:0:root:/root:/bin/bash
$> STRING="$(grep root /etc/passwd)"
$> echo $STRING
root:x:0:0:root:/root:/bin/bash