脚本判断命令
Shell常用特殊变量
经常会在shell命令中,看到$0, $#, $*, $@, $?, $$这样的取值,这些代表什么呢?
变量 | 含义 |
---|---|
$0 | 当前脚本的文件名 |
$n | 传递给脚本或函数的参数。n 是一个数字,表示第几个参数。例如,第一个参数是$1,第二个参数是$2 |
$# | 传递给脚本或函数的参数个数 |
$* | 传递给脚本或函数的所有参数 |
$@ | 传递给脚本或函数的所有参数。被双引号(” “)包含时,与 $* 稍有不同 |
$? | 上个命令的退出状态,或函数的返回值。成功返回0,失败返回1 |
$$ | 当前Shell进程ID。对于 Shell 脚本,就是这些脚本所在的进程ID |
$* 和 $@ 都是将参数一个一个返回
"$*"将所有参数当做一个整体字符串返回 , "$@"将参数一个一个返回
常用判断参数
在shell命令文件中还经常会看到类似与if [ -z "${SPARK_HOME}" ]; then这样的判断语句?是不是也和我一样很疑惑-z是什么含义?
下面是几个常见的参数,供查询使用:
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-a file exists. -b file exists and is a block special file . -c file exists and is a character special file . -d file exists and is a directory. -e file exists (just the same as -a). -f file exists and is a regular file . -g file exists and has its setgid(2) bit set . -G file exists and has the same group ID as this process. -k file exists and has its sticky bit set . -L file exists and is a symbolic link. -n string length is not zero. -o Named option is set on. -O file exists and is owned by the user ID of this process. -p file exists and is a first in , first out (FIFO) special file or named pipe. -r file exists and is readable by the current process. -s file exists and has a size greater than zero. -S file exists and is a socket. -t file descriptor number fildes is open and associated with a terminal device. -u file exists and has its setuid(2) bit set . -w file exists and is writable by the current process. -x file exists and is executable by the current process. -z string length is zero. |
判断命令
shell中除了有上边这样用来判断文件是否存在的参数,当然还有判断两个数是否相等这样更常规的命令
例如,if [ $# -gt 0 ]这样判断传入参数个数是否为0
命令 | 含义 |
---|---|
-eq | 等于 |
-ne | 不等于 |
-gt | 大于 |
-lt | 小于 |
ge | 大于等于 |
le | 小于等于 |