How to return the PID from a bash script executed from a bash script

Question

The get_pid() function below is intended to return the PID of daemon_itinerary.sh.

The script below is not in the same working directory as daemon_itinerary.sh.

#!/bin/bash

PID=""

get_pid() {
    PID='pidof daemon_itinerary.sh'
}

start() {
    echo "Restarting test_daemon"
    get_pid
    if [[ -z $PID ]]; then
        echo "starting test_daemon .."
        sh /var/www/bin/daemon_itinerary.sh &
        get_pid
        echo "done. PID=$PID"
    else
        echo "test_deamon is alrady running, PID=$PID"
    fi
}

case "$1" in
start)
    start
;;
...
*)
    echo "Usage: $0 {start|stop|restart|status}"
esac

*edit

Start is being passed in as a command line argument.

pidof daemon_itinerary.sh should be in backticks, not single quotes. — user2849202
– user2849202, Commented Jan 24, 2018 at 1:17
Make daemon_itinerary.sh executable (700) and call directly, not with 'sh'. Then use 'pidof -x daemon_itinerary.sh' — user2849202
– user2849202, Commented Jan 24, 2018 at 1:37
not really, as Roadawl suggested yous should use pidof -x daemon_itinerary.sh. To capture the PID in a variable it should be pid=$(pidof daemon_itinerary.sh). Please note the lower case on pid variable as PID is a reserved name in bash. — LMC
– LMC, Commented Jan 24, 2018 at 2:23

DON · Accepted Answer · 2018-01-24 04:28:31Z

4

we use pgrep to get the pid of a processm like below

PID=$(pgrep -f "daemon_itinerary.sh" | xargs)

# xargs - is given because pgrep will return both process id as well as parent pid
# also it will help us to get all pids if multiple instances are running.
# pgrep option to get session id or parent id alone, here its from manual
# -P, --parent ppid,...
#     Only match processes whose parent process ID is listed.
# -s, --session sid,...
#     Only match processes whose process session ID is listed. Session ID 0 is translated into pgrep's or pkill's own session ID.

edited Jan 24, 2018 at 4:28

answered Jan 24, 2018 at 4:11

DON

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