Shell execute multiple commands from string with ampersand(background process)

What you are after is what is called Asynchronous lists:

If a command is terminated by the control operator <ampersand> ( & ), the shell shall execute the command asynchronously in a subshell. This means that the shell shall not wait for the command to finish before executing the next command.

The format for running a command in the background is:

command1 & [command2 & ... ]

_{source: POSIX.1-2017}

The following example shows this behaviour:

sh -c "{ sleep 10 && echo foo ;} & echo bar"

This will execute echo bar and after 10 seconds, echo foo due to the command sleep 10 && echo foo. The latter is written as a compound command.

Thus, the solution is to remove the semi-column ; which is actually a sequential list. The reason why the original was failing is that you try to execute an empty command. This works:

sh -c "echo foo & echo bar ; echo car"

but this fails:

sh -c "echo foo &          ; echo car"

as there is syntactically a command missing.

So in the end, the solution is simple:

sh -c 'nohup ./server & echo foo'