什么是$ {0％/ *}在bash脚本的含义是什么？ [英] What is the meaning of ${0%/*} in a bash script?

问题描述

我想了解一个测试脚本，其中包括以下环节：

I am trying to understand a test script, which includes the following segment:

SCRIPT_PATH=${0%/*}
if [ "$0" != "$SCRIPT_PATH" ] && [ "$SCRIPT_PATH" != "" ]; then 
    cd $SCRIPT_PATH
fi

什么是 $ {0％/ *} 代表什么？谢谢

推荐答案

这就是所谓的 参数扩展 。看看本页面和网站的其余部分。

It is called Parameter Expansion. Take a look at this page and the rest of the site.

什么 $ {0％/ *} 所做的就是，它扩展包含在价值的参数0 的（这是路径称为取出后的字符串脚本） / * 从它的结束后缀。

What ${0%/*} does is, it expands the value contained within the argument 0 (which is the path that called the script) after removing the string /* suffix from the end of it.

因此​​， $ 0 相同 $ {0} 这就像任何其他的说法，例如。 $ 1 您可以为 $写{1} 。正如我所说的 $ 1,0 是特殊的，因为它不是一个的真正的说法，它总是在那里，并重新presents脚本的名称。参数扩建工程中的 { } - 花括号和％是一个类型参数扩展的。

So, $0 is the same as ${0} which is like any other argument, eg. $1 which you can write as ${1}. As I said $0 is special, as it's not a real argument, it's always there and represents name of script. Parameter Expansion works within the { } -- curly braces, and % is one type of Parameter Expansion.

％/ * 匹配 / 的最后次数，并删除任何东西（ * 表示字符后的任何东西）。看看这个简单的例子：

%/* matches the last occurance of / and removes anything (* means anything) after that character. Take a look at this simple example:

$ var="foo/bar/baz"
$ echo "$var"
foo/bar/baz
$ echo "${var}"
foo/bar/baz
$ echo "${var%/*}"
foo/bar

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