Crontab, as most people know, enables users to schedule commands or shell scripts to run periodically at certain times or dates.
The other day, this very useful Linux tool gave me a hard time! 🙁
Indeed, one of my commands wasn’t working in cron but was working perfectly fine when written in a shell console.
The faulty command looked like this:
0 5 * * 3 /data/script.sh > /data/script_`date +%y%m%d`.log 2>&1
If I run this command in a shell console, everything works fine and I get a log file containing today’s date in its filename. However, if I set this command line in my crontab, it doesn’t work and no log file is even created!
Reading the documentation of cron, I discovered the following statement:
Percent-signs (%) in the command, unless escaped with backslash (\), will be changed into newline characters, and all data after the first % will be sent to the command as standard input.
Well, this is good to know, isn’t it? 😉
We need to escape the percent-signs on our command line.
So in order to get our ‘faulty’ command to run in cron, it needs to look like the following:
0 5 * * 3 /data/script.sh > /data/script_`date +\%y\%m\%d`.log 2>&1