On Tue, Jun 29, 2021 at 10:23 PM L A Walsh <b...@tlinx.org> wrote:
> I hope a basic question isn't too offtopic.
> Say I have some number of jobs running:
>
> > jobs|wc -l
> 3
> ---
>
> Would like to pass a varname to njobs to store the answer in, like:
>
> So I can run:
>
> > njobs n
> echo "$n"
> 3
>
>
This a a double question 'how to', and I see no bash bugs here.
The 2 questions are
- how do I pass a variable name as an output argument to a function ('n' in
your 'jobs n' example)
- how to set a variable in a sub command? that is no doable, a sub command
can't return variable to its parent, so you obviously have to do things
diffrently.
A simple 2 liners, solve all this, with no code injection blah....
PW$ jobs
[1] Running sleep 11111111111 &
[2] Running sleep 11111111111 &
[3]- Running sleep 11111111111 &
[4]+ Running sleep 11111111111 &
PW$
PW$ function njobs
> { [ "$1" != "n" ] && typeset -n n="$1"
> typeset -a t ; readarray t <<<"$(jobs)" ;n=${#t[@]}
> }
PW$ njobs n ; echo $n
4
# explanations (you may skip here)
#===========================
[ "$1" != "n" ] && typeset -n n="$1"
This make sure the given output variable name is a valid SHELL identifier,
providing anything not valid in "$1" will break there.
This also enforce that the given $1 output variable name doesn't match our
own local nameref name, if it match we don't do our nameref, and re-use the
upper scope output variable name, that by definition is a valid variable
name if we got that far.
typeset -a t
define a local array that we will fill, being local mean the booking is
done at function return
readarray t <<<"$(jobs)" ;
Fill the array with your command you want to count lines for.
n=${#t[@]}
Fill the output variable
All is safe, all is clean, no 'apparent' temp file, no sub command :)
Shell programing is fun :)
