010#文件锁定

#!/bin/bash
# FILENAME：filelock

# 默认重试次数
retries="10"

# 默认操作
action="lock"

# 用于锁文件的空命令
nullcmd="‘which true‘"

# 设置选项
while getopts "lur:" opt; do
  case $opt in
    l) action="lock"     ;;
    u) action="unlock"   ;;
    r) action="$OPTARG"  ;;
  esac
done

shift $(($OPTIND - 1))
# $OPTIND 是参数指针(选项索引)

if [ $# -eq 0 ]; then
  cat<<EOF >&2
Usage: $0 [-l|-u] [-r retries] LOCKFILE
Where -l requests a lock (the default),
-u requests an unlock, -r X specifies a max
number of retries before it fails (default = $retries).
EOF
  exit 1
fi

# 确定是否有lockfile命令
if [ -z "$(which lockfile | grep -v ‘^no ‘)" ]; then
  echo "$0 failed: `lockfile` utility not found in PATH." >&2
  exit 1
fi

if [ "$action" = "lock" ]; then
  if ! lockfile -1 -r $retries "$1" 2>/dev/null; then
    echo "$0: Failed: Couldn‘t create lockfile in time." >&2
    exit 1
  fi
else
  if [ ! -f "$1" ]; then
    echo "$0: Warning: lockfile $1 doesn‘t exist to unlock." >&2
    exit 1
  fi
  rm -f "$1"
fi

exit 0