I want to restart celery from server, because the celery has many process, to I write this script to query all process id and kill it:

# stop celery process
PID=`ps -ef|grep -w ${CELERY_PROGRAM_NAME}|grep -v grep|cut -c 9-15`
if [ -z "${PID}" ]; then
  echo "Process aready down..."
    for var in "${array[@]}"
      single_pid=`echo ${var} | awk 'gsub(/^ *| *$/,"")' `
      if [[ ${single_pid} -gt 1 ]]; then
          kill -15 "${single_pid}"
          echo "Process ${PROGRAM_NAME} not found"

from the log, I found the pid did not convert to array, the next step did not split correctly. I run this script remotely from GitHub Actions. This is the log output from GitHub Actions:

cd /opt/apps/pydolphin
. /opt/apps/pydolphin/restart.sh

err: +/opt/apps/pydolphin/restart.sh:16> PROGRAM_NAME=schedulespider.py 
err: +/opt/apps/pydolphin/restart.sh:17> CELERY_PROGRAM_NAME=celery 
err: +/opt/apps/pydolphin/restart.sh:18> PYTHON_BIN_PATH=/usr/bin/python3 
err: +/opt/apps/pydolphin/restart.sh:23> PID=+/opt/apps/pydolphin/restart.sh:23> ps -ef
err: +/opt/apps/pydolphin/restart.sh:23> PID=+/opt/apps/pydolphin/restart.sh:23> grep -w celery
err: +/opt/apps/pydolphin/restart.sh:23> PID=+/opt/apps/pydolphin/restart.sh:23> grep -v grep
err: +/opt/apps/pydolphin/restart.sh:23> PID=+/opt/apps/pydolphin/restart.sh:23> cut -c 9-15
err: +/opt/apps/pydolphin/restart.sh:23> PID='  9777 
err:   9778 
err:   9779 
err:   9865 
err:   9867 
err:   9868 ' 
err: +/opt/apps/pydolphin/restart.sh:24> [ -z '  9777 
err:   9778 
err:   9779 
err:   9865 
err:   9867 
err:   9868 ' ']'
err: +/opt/apps/pydolphin/restart.sh:27> array=( '  9777 
err:   9778 
err:   9779 
err:   9865 
err:   9867 
err:   9868 ' ) 
err: +/opt/apps/pydolphin/restart.sh:28> var=  9777 
err:   9778 
err:   9779 
err:   9865 
err:   9867 
err:   9868 
err: +/opt/apps/pydolphin/restart.sh:30> single_pid=+/opt/apps/pydolphin/restart.sh:30> echo '  9777 
err:   9778 
err:   9779 
err:   9865 
err:   9867 
2021/07/19 06:00:52 Process exited with status 1
err:   9868 '
err: +/opt/apps/pydolphin/restart.sh:30> single_pid=+/opt/apps/pydolphin/restart.sh:30> awk 'gsub(/^ *| *$/,"")'
err: +/opt/apps/pydolphin/restart.sh:30> single_pid='9777
err: 9778
err: 9779
err: 9865
err: 9867
err: 9868' 
err: +/opt/apps/pydolphin/restart.sh:31> [[ '9777
err: 9778
err: 9779
err: 9865
err: 9867
err: 9868' -gt 1/opt/apps/pydolphin/restart.sh:31: bad math expression: operator expected at `9778\n9779\n...'
err:  ]]

I read my script and did not found where is going wrong, what should I do to make it work?

  • 4
    Do you have the pkill program available? – Jeff Schaller Jul 19 at 12:48
  • Yes, I could using pkill, but I still want to find where my code going wrong, I want to learn the bash.@JeffSchaller – Dolphin Jul 19 at 12:50
  • Is your interactive shell zsh? I noticed a ". /opt/apps/pydolphin/restart.sh" in your question and steeldriver's answer indicates that zsh could be playing a role. For future questions, be careful you know which shell is executing your code! (and word/tag questions appropriately). Thanks! – Jeff Schaller Jul 19 at 13:57
  • 1
    That xtrace output format suggests the script is interpreted by zsh, not bash. – Stéphane Chazelas Jul 19 at 14:28

If you are determined to write your own "kill loop" instead of simply using pkill, then at least use pgrep to get a list of PIDs, unencumbered by possible leading / trailing whitespace - instead of trying to slice and dice the output of ps:

array=($(pgrep -- "${CELERY_PROGRAM_NAME}"))

or simply loop over the pgrep output directly

for single_pid in $(pgrep -- "${CELERY_PROGRAM_NAME}"); do ...

pgrep produces a list of PIDs, one per line, and the default bash IFS will split on contiguous whitespace including newlines to map them to an array ex.

$ pgrep ssh

$ array=($(pgrep ssh))

$ declare -p array
declare -a array=([0]="1194" [1]="3688" [2]="22642" [3]="22754")

Alternatively could use readarray -t array < <(pgrep ssh).

There's no need to test for string emptiness since the loop will simply not run if there are no elements.

As to why your implementation is not working, ${PID//\n/} would remove literal n characters from PID1. Assuming PID only contains numeric values, that should do nothing, and array=(${PID//\n/}) should have created an array of individual PIDs, also removing leading and trailing whitespace so that further processing to get a single_pid should be unnecessary.

The fact that it apparently doesn't (based on your error output) suggests one of two causes:

  1. you have modified the shell's IFS value

  2. the shell you are using doesn't word-split unquoted variable expansions. zsh, which the format of your xtrace output suggests you're using has that default behavior for example, though does IFS-splitting upon command substitution, so the code above would still work in that shell. To split on newline in zsh, you'd rather use:

    array=(${(f)"$(pgrep -- $CELERY_PROGRAM_NAME)"})

    though, which like bash's readarray would remove the dependency on the current value of $IFS.

1 to actually remove newlines, you could use ${PID//$'\n'/}


another alternative to avoid pgrep/pkill is to customize ps's output.

ps can be customize in both process to list and format/fields to print.

note that ps -ef will list all process with many fields, and could be cumbersome to fetch pid.

while ps -e -o pid,comm will give a two columns output

   1 systemd
   2 kthreadd
   3 rcu_gp
   4 rcu_par_gp
   9 mm_percpu_wq
  10 ksoftirqd/0
1002 gdm3
1013 sshd
1031 php-fpm7.4
1032 php-fpm7.4
1044 nginx
1065 nmbd
     (many more lines)

(or -o pid= -o comm= to remove the headers).

If the process I am looking for is in ${CELERY_PROGRAM_NAME} (and doesn't contain backslash or blank characters), I can use

 ps -e -o pid= -o comm= | awk -v proc="${CELERY_PROGRAM_NAME}" '$2==proc { print $1}'

to fetch pids.


PID=$(ps -e -o pid= -o comm= | awk -v proc="${CELERY_PROGRAM_NAME}" '$2==proc { print $1})

after checking non emptiness, and given that ${PID} is a newline-delimited list of pids, I can use (assuming $IFS contains newline as it does by default):

for pid2 in ${PID}

(if using zsh as the format of your xtrace output suggests you do, replace ${PID} with ${=PID} to do $IFS-splitting like bash does by default, or with ${(f)PID} to split on newline regardless of the value of $IFS).


some select of ps (see man ps for all )

  • ps -p 1234 -o tty,args (list tty and args of pid 1234 )
  • ps -t pts/1,pts/3 -f (list all from tty pts/1 and pts/3 )
  • ps -u archemar (list all process belonging to archemar)

The HP/UX and procps implementations of ps also support a -C option to query processes based on their name.


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