Re: Problem expanding environment variables

[Silvio Knizek <killermoehre@xxxxxxx>]

Am Freitag, dem 06.09.2024 um 10:18 +0200 schrieb Thomas Köller:

> I am having problems expanding environment variables in a service file.  
> This test serivice illustrates the problem:
> 
> `root@yoga:/etc/systemd/system# cat varexp.service`
> 
> ```ini
> [Unit]
> Description = Test environment variable expansion
> 
> [Service]
> Type = oneshot
> Environment = "VAR=abc-xyz"
> ExecStart = sh -c 'echo Res: ${VAR#abc-}'
> ```
> 
> Running it yields the following result:
> 
> `root@yoga:/etc/systemd/system# systemctl status varexp.service`
> ```
> ○ varexp.service - Test environment variable expansion
>       Loaded: loaded (/etc/systemd/system/varexp.service; static)
>      Drop-In: /usr/lib/systemd/system/service.d
>               └─10-timeout-abort.conf
>       Active: inactive (dead)
> 
> Sep 06 10:17:16 yoga systemd[1]: Starting varexp.service - Test 
> environment variable expansion...
> Sep 06 10:17:16 yoga (sh)[8541]: varexp.service: Invalid environment 
> variable name evaluates to an empty string: VAR#abc-
> Sep 06 10:17:16 yoga sh[8541]: Res:
> Sep 06 10:17:16 yoga systemd[1]: varexp.service: Deactivated successfully.
> Sep 06 10:17:16 yoga systemd[1]: Finished varexp.service - Test 
> environment variable expansion.
> ```
> 
> According to the output lines above, it is the shell that complains. 
> However, running the command from an interactive shell yields the 
> expected result:
> 
> `root@yoga:/etc/systemd/system# VAR='abc-xyz' sh -c 'echo ${VAR#abc-}'`
> ```bash
> xyz
> ```
> 
> What is wrong here?

Hi Thomas,

`systemd` is trying to interpolate the variable `${VAR#abc-}` first before giving it to your `ExecStart=`.

Use `$${VAR#abc-}` instead.

BR  
Silvio