Bash variable change doesn't persist

Question

I have a short bash script to check to see if a Python program is running. The program writes out a PID file when it runs, so comparing this to the current list of running p

Answer 1

Commands after a pipe | are run in a subshell. Changes to variable values in a subshell do not propagate to the parent shell.

Solution: change your loop to

while read PID; do
    # ...
done < $PIDFILE

Answer 2

It's the pipe that is the problem. Using a pipe in this way means that the loop runs in a sub-shell, with its own environment. Kill the cat, use this syntax instead:

while read PID; do
    if [ $PID != "" ]; then
      PSGREP=$(ps -A | grep $PID | awk '{print $1}')
      if [ -n "$PSGREP" ]; then
        isRunning=1
        echo "RUNNING: $isRunning"
      fi
    fi
  done < "$PIDFILE"