在一个多变量替换 [英] multiple replacements on a single variable

问题描述

有关以下变量：

VAR =/路径/要/我的/文档001_extra.txt

我需要的 / [斜杠]之间以及 _ [下划线]只有部分。
此外， - [冲刺]需要被剥离

i need only the parts between the / [slash] and the _ [underscore]. Also, the - [dash] needs to be stripped.

在换句话说：文件001

这是我迄今为止：

VAR =$ {VAR ## * /}

VAR =$ {VAR％_ *}

VAR =$ {VAR / - /}

这工作得很好，但我在寻找，将饶了我一个更紧凑的替代模式的三重 VAR = ...

which works fine, but I'm looking for a more compact substitution pattern that would spare me the triple var=...

使用的SED，AWK，剪切等或许会更有意义，但我正在寻找一个纯bash的解决方案。

Use of sed, awk, cut, etc. would perhaps make more sense for this, but I'm looking for a pure bash solution.

根据需要GNU bash的工作，版本51年3月2日（1）-release

Needs to work under GNU bash, version 3.2.51(1)-release

推荐答案

编辑您的问题谈的模式，而不是常规的前pressions之后，现在我将告诉你如何的真正的使用常规的前pressions在庆典：）

After editing your question to talk about patterns instead of regular expressions, I'll now show you how to actually use regular expressions in bash :)

[[ $var =~ ^.*/(.*)-(.*)_ ]] && var="${BASH_REMATCH[@]:1:2}"

参数扩展就像你使用previously可惜不能嵌套在庆典（除非你用不明智的评估黑客，甚至然后它会比上面的线）不太清楚。

Parameter expansions like you were using previously unfortunately cannot be nested in bash (unless you use ill-advised eval hacks, and even then it will be less clear than the line above).

=〜运算符执行左边的字符串，并在右侧的普通前pression之间的匹配。在常规的前pression括号定义匹配组。如果匹配成功，退出状态 [...] 为零，因此code以下的＆安培; ＆安培; 被执行。 （提醒：不要混淆进程退出状态的0 =成功，非零=失败与公约的共同布尔约定0 =假1 =真。）

The =~ operator performs a match between the string on the left and the regular expression on the right. Parentheses in the regular expression define match groups. If a match is successful, the exit status of [[ ... ]] is zero, and so the code following the && is executed. (Reminder: don't confuse the "0=success, non-zero=failure" convention of process exit statuses with the common Boolean convention of "0=false, 1=true".)

BASH_REMATCH 是，在成功地定期-EX pression匹配庆典设置一个数组参数。该阵列的第一个元素包含由常规的前pression匹配全文;以下每个元素包含对应捕获组中的内容。

BASH_REMATCH is an array parameter that bash sets following a successful regular-expression match. The first element of the array contains the full text matched by the regular expression; each of the following elements contains the contents of the corresponding capture group.

的 $ {foo的[@]：X：Y} 参数扩展产生的数组是元素，从索引 X 。在这种情况下，它只是写的一小段路 $ {BASH_REMATCH [1]} $ {BASH_REMATCH [2]} 。 （另外，虽然 VAR = $ {BASH_REMATCH [*]：1：2} 会工作为好，我倾向于使用 @ 反正强化的事实，你几乎总是要使用 @ 而不是 * 在其他情况下。 ）

The ${foo[@]:x:y} parameter expansion produces y elements of the array, starting with index x. In this case, it's just a short way of writing ${BASH_REMATCH[1]} ${BASH_REMATCH[2]}. (Also, while var=${BASH_REMATCH[*]:1:2} would have worked as well, I tend to use @ anyway to reinforce the fact that you almost always want to use @ instead of * in other contexts.)

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