Watches a running process, executing a specified command when it finishes (Bash).

run_after_proc_exit.sh

#!/bin/bash
script="$(basename ${0})"
read -r -d '' USAGE <<-EOF

Watches a specified process (by pid or name) and runs
a specified command after it exits.
If watching by name, the command executes when no process 
by that name is running.

Usage:
  ${script}  [-a|-A] [-t seconds] pid  cmd
  ${script}  [-a|-A] [-t seconds] -n name  cmd
  ${script}  -h

     pid          the process id of the process to monitor
     cmd          a command to run when the monitored process exits
     -a           uses \`ps -a\` when searching for processes
     -A           uses \`ps -A\` when searching for processes
     -h           print this usage message and exit
     -n name      monitor for presence of any running process named  
                  \`name\`, not by pid
     -t seconds   set delay between polling attempts to \`seconds\` (default 5)
EOF

by_name=0
delay=5
dash_a=""

# process command arguments

while [[ "${1:0:1}" == "-" ]] ; do
    if [[ "${1}" == "-a" ]] || [[ "${1}" == "-A" ]] ; then
        dash_a="${1}"
        shift
    elif [[ "${1}" == "-n" ]] || [[ "${1}" == "--name" ]] ; then
        shift
        by_name=1
        name=${1}
        pid=${1}
        shift
    elif [[ "${1}" == "-t" ]] || [[ "${1}" == "--time" ]] ; then
        shift
        delay=${1}
        shift
    elif [[ "${1}" == "-h" ]] || [[ "${1}" == "--help" ]] ; then
        shift
        echo
        echo "${USAGE}"
        echo
        exit 0    
    fi
done

if [[ -z ${name} ]] ; then
    name="${1}"
    pid="${1}"
    shift
fi

cmd="$@"

# Do some sanity checking

if [[ -z ${pid} ]] || [[ -z ${cmd} ]] ; then
    echo
    echo "Error: Not enough arguments given."
    echo
    echo "${USAGE}"
    echo
    exit 1
fi

isint_re='^[0-9]+$'

if  [[ ${by_name} -eq 0 ]] && ! [[ ${pid} =~ ${isint_re} ]] ; then
    echo
    echo "Error: PID must be an integer. (Saw '${pid}'.)"
    echo
    echo "${USAGE}"
    echo
    exit 2
fi

if ! [[ ${delay} =~ ${isint_re} ]] ; then
    echo
    echo "Error: Delay must be an integer. (Saw '${delay}'.)"
    echo
    echo "${USAGE}"
    echo
    exit 3
fi

# Now we can do the work

echo "Waiting on ${pid}, then running: ${cmd}"
first_check=0

while true; do
        if [[ $by_name -ne 0 ]] ; then
            pid=$(ps ${dash_a} | grep -m1 -e "[0-9]\s*${name}" | awk '{print $1}')
        fi

        kill -0 $pid 2>/dev/null
        
        if [[ $? -ne 0 ]] ; then
            if [[ ${first_check} -ne 0 ]] ; then
                $cmd
                exit $?
            else
                echo 
                echo "Error:  The process '${name}' does not appear to be running!"
                echo "        Maybe you need the -a or -A option?"
                echo
                echo "${USAGE}"
                echo
                exit 4
            fi
        fi
        sleep ${delay}
        first_check=1
done