Linux Shell Scripting Cookbook - Third Edition

Silent output for grep

Sometimes, instead of examining at the matched strings, we are only interested in whether there was a match or not. The quiet option (-q), causes grep to run silently and not generate any output. Instead, it runs the command and returns an exit status based on success or failure. The return status is 0 for success and nonzero for failure.

The grep command can be used in quiet mode, for testing whether a match text appears in a file or not:

 #!/bin/bash #Filename: silent_grep.sh #Desc: Testing whether a file contain a text or not if [ $# -ne 2 ]; then echo "Usage: $0 match_text filename" exit 1 fi match_text=$1 filename=$2 grep -q "$match_text" $filename if [ $? -eq 0 ]; then echo "The text exists in the file" else echo ...