[linux] What is the best way to ensure only one instance of a Bash script is running?

first test example

[[ $(lsof -t $0| wc -l) > 1 ]] && echo "At least one of $0 is running"

second test example

currsh=$0
currpid=$$
runpid=$(lsof -t $currsh| paste -s -d " ")
if [[ $runpid == $currpid ]]
then
  sleep 11111111111111111
else
  echo -e "\nPID($runpid)($currpid) ::: At least one of \"$currsh\" is running !!!\n"
  false
  exit 1
fi

explanation

"lsof -t" to list all pids of current running scripts named "$0".

Command "lsof" will do two advantages.

  1. Ignore pids which is editing by editor such as vim, because vim edit its mapping file such as ".file.swp".
  2. Ignore pids forked by current running shell scripts, which most "grep" derivative command can't achieve it. Use "pstree -pH pidnum" command to see details about current process forking status.

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