快捷導(dǎo)航

對(duì)shell中常見(jiàn)參數(shù)及判斷命令介紹

更新時(shí)間：2018年07月14日 10:51:22 作者：hywelZhang

今天小編就為大家分享一篇對(duì)shell中常見(jiàn)參數(shù)及判斷命令介紹，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。一起跟隨小編過(guò)來(lái)看看吧

Shell常用特殊變量

經(jīng)常會(huì)在shell命令中，看到$0, $#, $*, $@, $?, $$這樣的取值，這些代表什么呢？

變量	含義
$0	當(dāng)前腳本的文件名
$n	傳遞給腳本或函數(shù)的參數(shù)。n 是一個(gè)數(shù)字，表示第幾個(gè)參數(shù)。例如，第一個(gè)參數(shù)是$1，第二個(gè)參數(shù)是$2
$#	傳遞給腳本或函數(shù)的參數(shù)個(gè)數(shù)
$*	傳遞給腳本或函數(shù)的所有參數(shù)
$@	傳遞給腳本或函數(shù)的所有參數(shù)。被雙引號(hào)(” “)包含時(shí)，與 $* 稍有不同
$?	上個(gè)命令的退出狀態(tài)，或函數(shù)的返回值。成功返回0，失敗返回1
$$	當(dāng)前Shell進(jìn)程ID。對(duì)于 Shell 腳本，就是這些腳本所在的進(jìn)程ID

$* 和 $@ 都是將參數(shù)一個(gè)一個(gè)返回

"$*"將所有參數(shù)當(dāng)做一個(gè)整體字符串返回 , "$@"將參數(shù)一個(gè)一個(gè)返回

常用判斷參數(shù)

在shell命令文件中還經(jīng)常會(huì)看到類似與if [ -z "${SPARK_HOME}" ]; then這樣的判斷語(yǔ)句？是不是也和我一樣很疑惑-z是什么含義？

下面是幾個(gè)常見(jiàn)的參數(shù)，供查詢使用：

-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.

判斷命令

shell中除了有上邊這樣用來(lái)判斷文件是否存在的參數(shù)，當(dāng)然還有判斷兩個(gè)數(shù)是否相等這樣更常規(guī)的命令

例如，if [ $# -gt 0 ]這樣判斷傳入?yún)?shù)個(gè)數(shù)是否為0