Special escaping for crontab [duplicate]

Question

I have the following user crontab entry on a RHEL 6 machine (sensitive values have been replaced):

[email protected]
0 5 * * * ~/bin/app_state.sh host-arg 9200 > ~/state/app-state-$(hostname)-$(date +%F).json

Which produces this entry in /var/log/cron:

Apr 23 05:00:08 host CROND[13901]: (dbjobs) CMD (~/bin/app_state.sh host-arg 9200 > ~/state/app-state-$(hostname)-$(date +)

But no file.

After changing the statement to:

43 5 * * * ~/bin/app_state.sh host-arg 9200 > ~/state/app-state-static.json

I get a better log entry and the file is created at ~/state/app-state-static.json

I'm sure there's some issue with not escaping the +%F but can't for the life of me find details of how I should be escaping it. I could wrap the filename generation inside another shell script but this is more easy to read for people coming looking for the file.

Kamal

Did you try to escape it like date +\%F – Flickertail

Btw, this question would be more appropriate on another site, e.g., superuser.com or unix.stackexchange.com (hence the close requests). – Flickertail

Documented in the crontab(5) man page. – Sofar

+\%F did the trick. I'll re ask on unix stack exchange so the answer can go on record but is there a clean way to close it out here? – Kamal

Now that you have your answer it's useless to ask it on another site (especially this might be a FAQ so your question might be tagged as duplicate). Just leave everything as it is! prosperity will tell. – Flickertail

The crontab tag wiki actually says "There are several reasons for why a cron job wouldn't run as expected: 1. Using percent signs, as in date +%F" – Wolenik

Answer 1

As crontab tag wiki says, percent characters are problematic in crontabs; % gets converted to a newline:

[..] > ~/state/app-state-$(hostname)-$(date +%F).json

would run command as

[..] > ~/state/app-state-$(hostname)-$(date +\nF).json

“Escaping” percent characters is possible, but the escape character gets executed in the command. A job like following would run the command with \ in front of percent character.

0 5 * * * ~/bin/app_state.sh host-arg 9200 > ~/state/app-state-$(hostname)-$(date +%F).json

One way to circumvent this problem is to have the command in a script and execute that as a cron job:

/usr/local/bin/app_state_cron.sh:

#!/bin/sh

~/bin/app_state.sh host-arg 9200 > ~/state/app-state-$(hostname)-$(date +%F).json

And in crontab:

0 5 * * * /bin/sh /usr/local/bin/app_state_cron.sh

Declarative