bash的数值代表和其它代表相反：0表示true；非0代表false。

#!/bin/sh
PIDFILE="pid"

# true=nginx进程运行 false=nginx进程未运行
checkRunning(){
    # -f true表示普通文件
    if [ -f "$PIDFILE" ]; then
       # -z 字符串长度为0true
       if  [ -z "`cat $PIDFILE`" ];then
        echo "ERROR: Pidfile '$PIDFILE' exists but contains no pid"
        return "1";
       fi
       PID="`cat ${PIDFILE}`"
       RET="`ps -p "${PID}"|grep nginx`"
       # -n 字符串长度不为0为true
       if [ -n "$RET" ];then
	     echo "${RET}"
         return "0";
       fi
    fi
    return "1";
}

checkT_F(){
  return 2
}

status(){
    if (checkRunning);then
         PID="`cat $PIDFILE`"
         echo "'$SERVICE_NAME' is running (pid '$PID')"
         exit 0
    fi
    echo "'$SERVICE_NAME' not running"
    exit 1
}

case "$1" in
  status)
    status
    ;;
  zz)
    if [ -z "123" ];then
      echo "123 lenhth is 0"
    else
      echo "123 length is not 0"
    fi
    ;;
  check)
    if checkT_F ;then
      echo '2 is true'
    else 
      echo '2 is flase'
    fi
  ;; 
  *)
esac