1

From Bash's manual (Controlling the Prompt]1):

\j the number of jobs currently managed by the shell.  

\$ If the effective uid is 0, #, otherwise $.

What I'd like is to set PS1 to

[some-string] $

when there are no jobs; and

[some-string]2 $

when there are 2 jobs.

How I could I achieve that?

If possible, the solution could be simple, with only basic Bash expansions and possibly Bash builtins.

2

I don't think Bash supports conditionals in the prompt (like e.g. screen does, IIRC), but you could use command substitution with \j to add some logic over it.

anyjobs() { [[ "$1" != 0 ]] && echo "[ $1 bg job(s) ] "; }
PS1='$? $(anyjobs \j)\u@\h \w\$ '

That does run a subshell, which involves a fork() in Bash, but I can't see a way around that.

In general, you could avoid the subshell by setting a variable in PROMPT_COMMAND, but I can't see a simple way to get the number of jobs there.

  • Many thx, really helpful. PROMPT_COMMAND? maybe similar to this (unix.stackexchange.com/a/217097/202329), though I cannot solve it currently. – qeatzy May 26 '18 at 11:25
  • @qeatzy, Bash runs whatever code there is in the PROMPT_COMMAND variable before printing each (primary) prompt. So you could set a variable there, and use it in PS1. E.g. something like PROMPT_COMMAND='((i += 3))'; PS1='$i \u@\h \w\$ ' (of course you can also call a function in PROMPT_COMMAND to make it cleaner) – ilkkachu May 26 '18 at 11:31
  • So yeah, pretty much what that answer also does. Though with the 7-line case in there, I'd definitely put it in a function. – ilkkachu May 26 '18 at 11:34
  • indeed, the function solution is cleaner. – qeatzy May 26 '18 at 11:35

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