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execute arbitrary bash code/variable substitution in systemd units
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| [Unit] | |
| Description=Demonstrate Bash | |
| [Service] | |
| ExecStartPre=/usr/bin/bash -c "/usr/bin/systemctl set-environment MYVAR=$(( 2 + 2 ))" | |
| ExecStart=/usr/bin/echo "2 + 2 = ${MYVAR}" |
Beware that there's a pitfall if you have to use %s with your command.
echo (date +%s)
SystemD sees this as user shell and resolve to /bin/sh instead. You need to use %%s to avoid that.
EnvironmentFile=/tmp/timestamp.txt
ExecStartPre=/bin/bash -c "echo TIMESTAMP=$(date +%%s) > /tmp/timestamp.txt;"
Although this seems simple, it was quite hard to find this info. ChatGPT was not yielding a correct result either.
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Thanks. I use it to finally make tigervnc work with SDDM:
https://gist.github.com/mjtiempo/8662e88da74236c58115bed5cc78ceaf