shell脚本是防止多次运行

#!/bin/bash
#
# file locking using bash.
# ver 0.1.6
#
# author : malundao ( [email protected] )
# date   : 2011-08-31   
# ref    : http://unix.derkeiler.com/Newsgroups/comp.unix.shell/2005-09/0472.html
#
# note:
#   shflock_cleanhook() is a user defined function to clean up user-specific sth.
#
# /path/to/lock/. note; directory, not a file.
# should be modified 
LOCKPATH="/tmp"
cleanup() {
        shflock_cleanhook
        cd $LOCKPATH
        [ -e lock.pid ] || exit
        read pid >/dev/null 2>&1  lock.$$
                [ -e lock.pid ] 
        do
                rm lock.$$
                read pid >/dev/null 2>&1 /dev/null 2>&1
        if [ $? -eq 0 ]; then
                cd $oldpath
                return 0 # We got the lock
        else
                [ -e lock.pid ] || echo WARN: please delete hanging lock.pid by HAND.
                cd $oldpath
                return 3 # Lock is probably taken by others.
        fi
}
putlock () {
    oldpath=`pwd`
    cd $LOCKPATH && rm -f lock.$$ lock.pid
    cd $oldpath
}
## test 
shflock_cleanhook() {
    echo i\'m a hook.
}
while true; do
    while ! getlock; do
        #echo wait a second...
        sleep 1
    done
    echo \[$$\] `date` ,now hold lock for 3 seconds...
    sleep 3
    #echo putlock
    putlock
    sleep 1 # yield
done