What does "| |" mean in a script

rollo · 11-23-2006, 06:07 PM

5-second question here. What does the "||" mean in a script, like this one:

Code:

test -x /usr/sbin/anacron || run-parts --report /etc/cron.weekly

(Tricky searching this one because the character in question is ignored by search engines.)

gilead · 11-23-2006, 06:12 PM

It means "or". If the left hand side returns a non-zero error code, the right hand side is run. This is complementary to && "and" where the right hand side is run if the left hand side returns no error (error code 0).

In this case, if /usr/sbin/anacron is not executable, then run-parts --report /etc/cron.weekly is executed

indienick · 11-23-2006, 06:15 PM

two pipes, ||, is the almost universal logical OR operator.

literal: this or that
programming: this || that

that code snippet tests if /usr/sbin/anacron is an executable, and should that test fail (for any reason, the file not exist, or the file is not executable) "run-parts --report /etc/cron.weekly" is executed.

rollo · 11-23-2006, 06:15 PM

Thanks gilead!

I understand now.

rollo · 11-23-2006, 06:17 PM

Thanks for the clarification, indynick.

matthewg42 · 11-23-2006, 07:01 PM

Because many programs set the return status to 0 if they are successful (a notable exception being grep), it's common to see something like this in a script:

Code:

some_command || exit 3

which would cause the script to exit with it's own non-zero status. in this case 3.

jschiwal · 11-23-2006, 08:06 PM

Grep works.

For example:
grep 'urlpoop' stupidwebpage.html && echo 'Found the stupid word'

Will return 0 if the regex is found and the echo command will be run. If it isn't found, the echo command will be skipped.