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 (1): [executing a sh script from the cron](http://unix.stackexchange.com/questions/6790/executing-a-sh-script-from-the-cron/6794#6794) — slm, Mar 26 '14 at 01:59
Related (2): [Frustrating issue where neither cron nor su -c runs my job (permissions?)](http://unix.stackexchange.com/questions/31117/frustrating-issue-where-neither-cron-nor-su-c-runs-my-job-permissions/31120#31120) — 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?](http://unix.stackexchange.com/questions/9880/why-does-crontab-give-me-an-error-with-my-php-script-when-running-it-from-the-te/9924#9924) — 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

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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

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answered May 26 '20 at 07:06

Bogus-bill

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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