I execute the following line in a bash console.
/bin/bash -c "echo `date` random=$((RANDOM % 10)) > /tmp/my.log"
The content of my.log is as expected.
Mo Aug 24 14:37:04 CEST 2020 random=6
Now I change the timestamp to epoch (format-code +%s).
/bin/bash -c "echo `date +%s` random=$((RANDOM % 10)) > /tmp/my.log"
File is
1598272710 random=3
As expected again.
But if I put this command line into systemd it would fail.
[Service] ExecStart=/bin/bash -c "echo `date +%s` random=$((RANDOM % 10)) > /tmp/my.log"
produces
/bin/sh random=7
Must be a problem with the format-code of date. If I remove the +%s then it is as expected (normal date-format and no epoch) with systemd too.
Any suggestions what is wrong with my command? Thanks!
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Answer
The %-secuences are replaced by systemd. From systemd.unit manual:
Specifiers
“%s” User shell This is the shell of the user running the service manager instance. In case of the system manager this resolves to “/bin/sh”.
%s is substituted for /bin/sh, and date +/bin/sh returns /bin/sh.
Do:
ExecStart=/bin/bash -c "echo $(date +%%s) random=$((RANDOM %% 10)) > /tmp/my.log"
Using backticks ` is discouraged. Use $(...) instead. bash hackers wiki deprecated and obsolete syntax