什么 $? $0 $1 $2在 shell 脚本中是什么意思？

我经常在 shell 脚本中遇到 $? $0 $1 $2 etc....，我所知道的是 $?返回最后一个命令的退出状态

echo "this will return 0"
echo $?

但是其他人做什么呢? 他们叫什么? 还有更多吗? 也许是3美元4美元5美元..。

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小开

These are positional arguments of the script.

Executing

./script.sh Hello World

Will make

$0 = ./script.sh
$1 = Hello
$2 = World

Note

If you execute ./script.sh, $0 will give output ./script.sh but if you execute it with bash script.sh it will give output script.sh.

小开

They are called the Positional Parameters.

3.4.1 Positional Parameters

A positional parameter is a parameter denoted by one or more digits, other than the single digit 0. Positional parameters are assigned from the shell’s arguments when it is invoked, and may be reassigned using the set builtin command. Positional parameter N may be referenced as ${N}, or as $N when N consists of a single digit. Positional parameters may not be assigned to with assignment statements. The set and shift builtins are used to set and unset them (see Shell Builtin Commands). The positional parameters are temporarily replaced when a shell function is executed (see Shell Functions).

When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces.