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I was reading a book about Linux. It states that to bring a process to foreground, use the fg command and a percent sign (%) followed by the job number. I did some testing and found that it works as expected. But I also found that I can use a simple number as the jobspec, like fg 3 (instead of fg %3), which can bring the third process to foreground, too. Is a simple number can be considered a valid jobspec?

Fajela Tajkiya
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  • In Bash, any of fg 3, fg %3 or %3 will bring job [3] back to foreground. If there is only one background job, fg will also bring it back. Regardless of the specification, none of those versions is ambiguous. – Paul_Pedant Apr 11 '22 at 10:12

1 Answers1

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Bash seems to accept fg 3 etc., but I'm not sure the documentation is too explicit about that.

The description for fg just says it takes a "jobspec", and their description says "The character ‘%’ introduces a job specification (jobspec)." and the % seems included in all the examples.

The other shells I tried (Dash, ksh and zsh) didn't accept a plain number there, so it looks like a Bash-only thing.

Note that kill can take a jobspec or a process ID, so both kill %3 and kill 3 are valid, they just mean different things. Which also implies that in general, a plain number can't work as a jobspec, so perhaps better to stick with %3.

ilkkachu
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