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.
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 "[ $1 bg job(s) ] "; } PS1='$? $(anyjobs \j)\u@\h \w\$ ' That does run a subshell, which involves a fork() in Bash, but I can't see a way around that.
In general, you could avoid the subshell by setting a variable in PROMPT_COMMAND, but I can't see a simple way to get the number of jobs there.
PROMPT_COMMAND variable before printing each (primary) prompt. So you could set a variable there, and use it in PS1. E.g. something like PROMPT_COMMAND='((i += 3))'; PS1='$i \u@\h \w\$ ' (of course you can also call a function in PROMPT_COMMAND to make it cleaner) case in there, I'd definitely put it in a function.