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Top Forums Shell Programming and Scripting Grep -q -F , what is the function of this script Post 303022807 by Aia on Friday 7th of September 2018 12:55:49 PM
Old 09-07-2018
Quote:
Originally Posted by Scott
Hello, Boris.

If "quiet" (-q) isn't used then grep will print any text it finds, to standard output (you can, similarly, make it "quiet" using [b]grep ... >/dev/null[/b]). Using -q does not affect the return code of the command. That's what's captured with ||. Using || is telling the shell to execute whatever follows, if grep fails (returns a non-zero return code). If you want to execute the "/bin/sh..." on a successful grep match, you should use && instead. Sometimes with these multi-line type of commands, it's simpler just to use an if statement.
grep -q is more than just suppressing any output, it will exist with success as soon as it finds a match, avoiding to continue searching any other lines in the file until it reaches the end of the file. Therefore
grep ... > /dev/null will not be the same
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