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Can a bash script tell if it's being run via cron?

Answer 1

+1 A:

Not without outside help, but it can tell if it's running from an interactive shell, which it will be when you're running it manually to test it:

if [ -z "$PS1" ]; then
        echo This shell is not interactive
else
        echo This shell is interactive
fi

(Code sample from here)

moonshadow 2010-07-09 17:12:51

This is perfect! Ideally I'd like it to work for anyone who runs it manually. Thank you very much!

Topher Fangio 2010-07-09 19:01:07

Answer 2

+2 A:

you can try "tty" to see if it's run by a terminal or not. that won't tell you that it's specifically run by cron, but you can tell if its "not a user as a prompt".

you can also get your parent-pid and follow it up the tree to look for cron, though that's a little heavy-handed.

eruciform 2010-07-09 17:14:11

Thanks for this answer! The former answer I picked was actually not what I wanted (interactive shell). Due to your answer, I found what I really needed by Googling "bash tty test". Basically, call `tty -s` in your script and then check `$?`: if it is 0, you are in a tty, if it's greater than 0, you aren't.

Topher Fangio 2010-08-03 15:52:30

Answer 3

+4 A:

Why not have a command line argument that is -t for testing or -c for cron.

Or better yet:

[email protected]

If it's not specified, don't send an email.

sims 2010-07-09 17:14:36

I'm dropping the script in /etc/cron.daily so I can't easily add arguments, but I guess I could move it to a real crontab. I was just hoping not to have to add arguments or set environment variables on the command line...although: setting a TESTING environment variable in my .bashrc file would do the trick.Thanks for the suggestions.

Topher Fangio 2010-07-09 18:59:30

There is no problem with putting myscript.sh arg1 arg2 arg3 in a script file in /etc/cron.daily. I don't usually put my script/binary file directly into the /etc/cron.* dirs. I usually leave that for scripts that execute the cron job (may be another script). Then I can write my script more generic and usable in other environments.

sims 2010-07-12 00:51:35

Answer 4

+1 A:

Here's two different options for you:

Take the emailing out of your script/program and let cron handle it. If you set the MAILTO variable in your crontab, cron will send anything printed out to that email address. eg:
```
[email protected]
# run five minutes after midnight, every day
5 0 * * *       $HOME/bin/daily.job
```

Set an environment variable in your crontab that is used to determine if running under cron. eg:

THIS_IS_CRON=1
# run five minutes after midnight, every day
5 0 * * *       $HOME/bin/daily.job

and in your script something like

if [ -n "$THIS_IS_CRON" ]; then echo "I'm running in cron"; else echo "I'm not running in cron"; fi

Geoff Reedy 2010-07-09 17:33:23

Answer 5

A:

Parse the process table (ps) to see whether the cron daemon is an ancestor of your process.

mobrule 2010-07-09 18:24:07

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Can a bash script tell if it's being run via cron?

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