How to define variables in a bash script run by Jenkins?

Question

bash

I have a conditional script that checks for a process on port 8080, writes its id to a variable, and kills by the value of that variable. When run through the standard shell, everything works fine. But when I run this file through jenkins (in the build -> execute shell section I write the full path to the file), then this variable turns out to be empty.
Here is an example script:

#$/bin/sh
for i in 1 2 3 4 5
do
  echo "Looping ... number $i"
done

pid="$(/usr/bin/lsof -ti tcp:8080)"
echo $pid

when run from bash, all variables are shown, when run via jenkins, only variables from 1 to 5 are shown, and 'pid' is not displayed.
How to correctly define a variable?

Answer 1

first, through jenkins, simply execute
/usr/bin/lsof -ti tcp:8080
make sure that the command returns PID
and then solve it, the command does not work or the variable is not passed

Answer 2

The lsof command doesn't really work; I'll look into that direction, thanks!