【shell 】 test, /usr/bin/test, [ ], 和/usr/bin/[都是等价命令

 test, /usr/bin/test, [ ], 和/usr/bin/[都是等价命令
#!/bin/bash  
echo
 if test -z "$1"
   then
     echo "No command-line arguments."
   else
     echo "First command-line argument is $1."
 fi
  echo
  if /usr/bin/test -z "$1"      # 与内建的"test"命令结果相同.
  then
    echo "No command-line arguments."
  else
    echo "First command-line argument is $1."
  fi
  echo  
  if [ -z "$1" ]                # 与上边的代码块作用相同.
  #   if [ -z "$1"                应该能够运行, 但是...
  #+  Bash报错, 提示缺少关闭条件测试的右中括号.
  then
    echo "No command-line arguments."
  else
    echo "First command-line argument is $1."
  fi
  
  echo
  
  
  if /usr/bin/[ -z "$1" ]       # 再来一个, 与上边的代码块作用相同.
  # if /usr/bin/[ -z "$1"       # 能够工作, 但是还是给出一个错误消息.
"vartify.sh" [New] 46L, 1086C written
root@client.example.com ~/yang # chmod 755 vartify.sh
root@client.example.com ~/yang # ./vartify.sh       
No command-line arguments.
No command-line arguments.
No command-line arguments.
No command-line arguments.
root@client.example.com ~/yang # ./vartify.sh yangqilong
First command-line argument is yangqilong.
First command-line argument is yangqilong.
First command-line argument is yangqilong.
First command-line argument is yangqilong.
root@client.example.com ~/yang #