if [ 1 -ne $(/bin/fuser "$0" 2>/dev/null | wc -w) ]; then
    exit 1
fi

这个我在任何地方都没有发现，它使用read，我不确切地知道read是否实际上是原子的，但到目前为止它对我来说很有用……它很有趣，因为它只是bash内置的，这是一个进程内实现，你启动locker协进程并使用它的I / O来管理锁，同样可以在进程间完成，只需将目标I / O从locker文件描述符交换到文件系统上的文件描述符(exec 3<>/file && exec 4</file)

## gives locks
locker() {
    locked=false
    while read l; do
        case "$l" in
            lock)
                if $locked; then
                    echo false
                else
                    locked=true
                    echo true
                fi
                ;;
            unlock)
                if $locked; then
                    locked=false
                    echo true
                else
                    echo false
                fi
                ;;
            *)
                echo false
                ;;
        esac
    done
}
## locks
lock() {
    local response
    echo lock >&${locker[1]}
    read -ru ${locker[0]} response
    $response && return 0 || return 1
}

## unlocks
unlock() {
    local response
    echo unlock >&${locker[1]}
    read -ru ${locker[0]} response
    $response && return 0 || return 1
}

又快又脏?

#!/bin/sh

if [ -f sometempfile ]
  echo "Already running... will now terminate."
  exit
else
  touch sometempfile
fi

..do what you want here..

rm sometempfile

羊群走的路才是正确的。想想当脚本突然失效时会发生什么。在羊群的情况下，你只是松散的羊群，但这不是一个问题。另外，请注意，一个邪恶的伎俩是在脚本本身取一群。但这当然会让您完全陷入权限问题。

对于shell脚本，我倾向于使用mkdir而不是flock，因为它使锁更可移植。

不管怎样，使用set -e是不够的。它只在任何命令失败时退出脚本。你的锁还是会留下的。

为了正确的锁清理，你真的应该把你的陷阱设置成这样的伪代码(提取，简化和未经测试，但来自积极使用的脚本):

#=======================================================================
# Predefined Global Variables
#=======================================================================

TMPDIR=/tmp/myapp
[[ ! -d $TMP_DIR ]] \
    && mkdir -p $TMP_DIR \
    && chmod 700 $TMPDIR

LOCK_DIR=$TMP_DIR/lock

#=======================================================================
# Functions
#=======================================================================

function mklock {
    __lockdir="$LOCK_DIR/$(date +%s.%N).$$" # Private Global. Use Epoch.Nano.PID

    # If it can create $LOCK_DIR then no other instance is running
    if $(mkdir $LOCK_DIR)
    then
        mkdir $__lockdir  # create this instance's specific lock in queue
        LOCK_EXISTS=true  # Global
    else
        echo "FATAL: Lock already exists. Another copy is running or manually lock clean up required."
        exit 1001  # Or work out some sleep_while_execution_lock elsewhere
    fi
}

function rmlock {
    [[ ! -d $__lockdir ]] \
        && echo "WARNING: Lock is missing. $__lockdir does not exist" \
        || rmdir $__lockdir
}

#-----------------------------------------------------------------------
# Private Signal Traps Functions {{{2
#
# DANGER: SIGKILL cannot be trapped. So, try not to `kill -9 PID` or 
#         there will be *NO CLEAN UP*. You'll have to manually remove 
#         any locks in place.
#-----------------------------------------------------------------------
function __sig_exit {

    # Place your clean up logic here 

    # Remove the LOCK
    [[ -n $LOCK_EXISTS ]] && rmlock
}

function __sig_int {
    echo "WARNING: SIGINT caught"    
    exit 1002
}

function __sig_quit {
    echo "SIGQUIT caught"
    exit 1003
}

function __sig_term {
    echo "WARNING: SIGTERM caught"    
    exit 1015
}

#=======================================================================
# Main
#=======================================================================

# Set TRAPs
trap __sig_exit EXIT    # SIGEXIT
trap __sig_int INT      # SIGINT
trap __sig_quit QUIT    # SIGQUIT
trap __sig_term TERM    # SIGTERM

mklock

# CODE

exit # No need for cleanup code here being in the __sig_exit trap function

接下来会发生什么。所有陷阱都会产生一个出口，所以__sig_exit函数总是会发生(除非SIGKILL)，它会清理你的锁。

注意:我的退出值不是低值。为什么?各种批处理系统生成或期望数字0到31。将它们设置为其他内容，我可以让我的脚本和批处理流对前一个批处理作业或脚本做出相应的反应。

下面是一种方法，它结合了原子目录锁定和通过PID检查过期锁，如果过期就重新启动。此外，这并不依赖于任何羞怯。

#!/bin/dash

SCRIPTNAME=$(basename $0)
LOCKDIR="/var/lock/${SCRIPTNAME}"
PIDFILE="${LOCKDIR}/pid"

if ! mkdir $LOCKDIR 2>/dev/null
then
    # lock failed, but check for stale one by checking if the PID is really existing
    PID=$(cat $PIDFILE)
    if ! kill -0 $PID 2>/dev/null
    then
       echo "Removing stale lock of nonexistent PID ${PID}" >&2
       rm -rf $LOCKDIR
       echo "Restarting myself (${SCRIPTNAME})" >&2
       exec "$0" "$@"
    fi
    echo "$SCRIPTNAME is already running, bailing out" >&2
    exit 1
else
    # lock successfully acquired, save PID
    echo $$ > $PIDFILE
fi

trap "rm -rf ${LOCKDIR}" QUIT INT TERM EXIT


echo hello

sleep 30s

echo bye