How to run a command as if it is called from cron

Question

I write a script and set it as a cron job. But due to a difference of environment variables it doesn't work as it should be.

In that case I change a little bit with crontab -e and set a cron job time closest minute, and wait next minute to come to show the result. I feel this is a totally absurd approach, but I don't know better way to do it.

If there is a way to run a script as if it is called inside cron job, I'm going to use it.

Does anyone know how to do it?

You could grab the environment from cron by scheduling env to run... — derobert, Mar 26 '14 at 00:54
Related (2): Frustrating issue where neither cron nor su -c runs my job (permissions?) — slm, Mar 26 '14 at 02:01
Related (3): Why does Crontab give me an error with my PHP script when running it from the terminal does not? — slm, Mar 26 '14 at 02:02
If you want to debug cron, just redirect the error output, run this with it your_script.sh 2>/path/to/logfile, that should help you understand what's going on. — terdon, Mar 26 '14 at 02:18

score 5 · Accepted Answer · answered Mar 26 '14 at 00:38

5

Here is how to do the other way around: forcing cron execution to use your login environment:

bash -lc "your_command"

From the bash manual:

-c string     If the -c option is present, then commands are read from string.
              If there are arguments after the string, they are assigned to the
               positional parameters, starting with $0.
-l            Make bash act as if it had been invoked as a login shell
               (see INVOCATION below).

INVOCATION (a bit stripped):

When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.

To known more:

man bash

answered Mar 26 '14 at 00:38

Ouki

5,962

Cron does not invoke the shell as a login shell when launching commands. – phemmer Mar 26 '14 at 01:24
That's why forcing it with bash -l option. – Ouki Mar 26 '14 at 01:43
Oh, I misunderstood what you were saying. While this works, I wouldn't consider it a very elegant solution :-/ – phemmer Mar 26 '14 at 01:46
1

Sure. The elegant thing would be to tune whatever environment set for cron ... – Ouki Mar 26 '14 at 01:48
Wouldn't --norc be closer to what cron runs? – terdon Mar 26 '14 at 02:58

score 2 · Answer 2 · edited May 26 '20 at 07:25

2

Another way would be:

/usr/bin/env --ignore-environment your command

From the manpage of env:

-i, --ignore-environment

start with an empty environment

edited May 26 '20 at 07:25

AdminBee

22,803

answered May 26 '20 at 07:06

Bogus-bill

21

score -1 · Answer 3 · 2014-03-26T01:07:27.883

-1

A better way is to use at.

Here are some examples

 echo $PWD/script.sh | at now

or

 echo "reboot" | at 5:00

or

 echo "mail -s test user@host" | at now + 1 hour

Here are some date/time Examples

edited Mar 26 '14 at 01:07

answered Mar 26 '14 at 00:59

I don't see the point here to play with at – Ouki Mar 26 '14 at 01:45
@Ouki take a look at /var/spool/cron/ – Mar 26 '14 at 02:21
and it's POSIX also – Mar 26 '14 at 21:18
at retains the working directory and environment at invocation, so it does not run as if from cron. – Ajit George Apr 08 '20 at 17:01

How to run a command as if it is called from cron

3 Answers3