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[#]: collector: (lujun9972)
[#]: translator: (geekpi)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Regex groups and numerals)
[#]: via: (https://leancrew.com/all-this/2019/02/regex-groups-and-numerals/)
[#]: author: (Dr.Drang https://leancrew.com)
Regex groups and numerals
======
A week or so ago, I was editing a program and decided I should change some variable names. I thought it would be a simple regex find/replace, and it was. Just not as simple as I thought.
The variables were named `a10`, `v10`, and `x10`, and I wanted to change them to `a30`, `v30`, and `x30`, respectively. I brought up BBEdit’s Find window and entered this:
![Mistaken BBEdit replacement pattern][2]
I couldn’t just replace `10` with `30` because there were instances of `10` in the code that weren’t related to the variables. And because I think I’m clever, I didn’t want to do three non-regex replacements, one each for `a10`, `v10`, and `x10`. But I wasn’t clever enough to notice the blue coloring in the replacement pattern. Had I done so, I would have seen that BBEdit was interpreting my replacement pattern as “Captured group 13, followed by `0`” instead of “Captured group 1, followed by `30`,” which was what I intended. Since captured group 13 was blank, all my variable names were replaced with `0`.
You see, BBEdit can capture up to 99 groups in the search pattern and, strictly speaking, we should use two-digit numbers when referring to them in the replacement pattern. But in most cases, we can use `\1` through `\9` instead of `\01` through `\09` because there’s no ambiguity. In other words, if I had been trying to change `a10`, `v10`, and `x10` to `az`, `vz`, and `xz`, a replacement pattern of `\1z` would have been just fine, because the trailing `z` means there’s no way to misinterpret the intent of the `\1` in that pattern.
So after undoing the replacement, I changed the pattern to this,
![Two-digit BBEdit replacement pattern][3]
and all was right with the world.
There was another option: a named group. Here’s how that would have looked, using `var` as the pattern name:
![Named BBEdit replacement pattern][4]
I don’t think I’ve ever used a named group in any situation, whether the regex was in a text editor or a script. My general feeling is that if the pattern is so complicated I have to use variables to keep track of all the groups, I should stop and break the problem down into smaller parts.
By the way, you may have heard that BBEdit is celebrating its [25th anniversary][5] of not sucking. When a well-documented app has such a long history, the manual starts to accumulate delightful callbacks to the olden days. As I was looking up the notation for named groups in the BBEdit manual, I ran across this note:
![BBEdit regex manual excerpt][6]
BBEdit is currently on Version 12.5; Version 6.5 came out in 2001. But the manual wants to make sure that long-time customers (I believe it was on Version 4 when I first bought it) don’t get confused by changes in behavior, even when those changes occurred nearly two decades ago.
--------------------------------------------------------------------------------
via: https://leancrew.com/all-this/2019/02/regex-groups-and-numerals/
作者：[Dr.Drang][a]
选题：[lujun9972][b]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://leancrew.com
[b]: https://github.com/lujun9972
[1]: https://leancrew.com/all-this/2019/02/automation-evolution/
[2]: https://leancrew.com/all-this/images2019/20190223-Mistaken%20BBEdit%20replacement%20pattern.png (Mistaken BBEdit replacement pattern)
[3]: https://leancrew.com/all-this/images2019/20190223-Two-digit%20BBEdit%20replacement%20pattern.png (Two-digit BBEdit replacement pattern)
[4]: https://leancrew.com/all-this/images2019/20190223-Named%20BBEdit%20replacement%20pattern.png (Named BBEdit replacement pattern)
[5]: https://merch.barebones.com/
[6]: https://leancrew.com/all-this/images2019/20190223-BBEdit%20regex%20manual%20excerpt.png (BBEdit regex manual excerpt)

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[#]: collector: (lujun9972)
[#]: translator: (geekpi)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Regex groups and numerals)
[#]: via: (https://leancrew.com/all-this/2019/02/regex-groups-and-numerals/)
[#]: author: (Dr.Drang https://leancrew.com)
正则组和数字
======
大约一周前，我在编辑一个程序时想要更改一些变量名。我之前认为这将是一个简单的正则表达式查找/替换。只是这没有我想象的那么简单。
变量名为 `a10`、`v10` 和 `x10`，我想分别将它们改为 `a30`、`v30` 和 `x30`。我想到使用 BBEdit 的查找窗口并输入：
![Mistaken BBEdit replacement pattern][2]
我不能简单地 `30` 替换为 `10`，因为代码中有一些与变量无关的数字 `10`。我认为我很聪明，所以我不想写三个非正则表达式替换，`a10`、`v10` 和 `x10` 每个一个。但是我却没有注意到替换模式中的蓝色。如果我这样做了，我会看到 BBEdit 将我的替换模式解释为“匹配组 13，后面跟着 `0`，而不是”匹配组 1，后面跟着 `30`，后者是我想要的。由于匹配组 13 是空白的，因此所有变量名都会被替换为 `0`。
你看，BBEdit 可以在搜索模式中匹配多达 99 个组，严格来说，我们应该在替换模式中引用它们时使用两位数字。但在大多数情况下，我们可以使用 `\1` 到 `\9` 而不是 `\01` 到 `\09`，因为这没有歧义。换句话说，如果我尝试将 `a10`、`v10` 和 `x10` 更改为 `az`、`vz` 和 `xz`，那么使用 `\1z`的替换模式就可以了。因为后面的 `z` 意味着不会误解释该模式中 `\1`。
因此，在撤消替换后，我将模式更改为这样：
![Two-digit BBEdit replacement pattern][3]
它可以正常工作。
还有另一个选择：命名组。这是使用 `var` 作为模式名称：
![Named BBEdit replacement pattern][4]
在任何情况下，我从来都没有使用过命名组，无论正则表达式是在文本编辑器还是在脚本中。我的总体感觉是，如果模式复杂到我必须使用变量来跟踪所有组，那么我应该停下来并将问题分解为更小的部分。
By the way, you may have heard that BBEdit is celebrating its [25th anniversary][5] of not sucking. When a well-documented app has such a long history, the manual starts to accumulate delightful callbacks to the olden days. As I was looking up the notation for named groups in the BBEdit manual, I ran across this note:
顺便说一下，你可能已经听说 BBEdit 正在庆祝它诞生[25周年][5]。当一个有良好文档的应用有如此历史时，手册的积累能让人愉快地回到过去的日子。当我在 BBEdit 手册中查找命名组的表示法时，我遇到了这个说明：
![BBEdit regex manual excerpt][6]
BBEdit 目前的版本是 12.5。第一次出现于 2001 年的 V6.5。但手册希望确保长期客户（我记得是在 V4 的时候第一次购买）不会因行为变化而感到困惑，即使这些变化几乎发生在二十年前。
--------------------------------------------------------------------------------
via: https://leancrew.com/all-this/2019/02/regex-groups-and-numerals/
作者：[Dr.Drang][a]
选题：[lujun9972][b]
译者：[geekpi](https://github.com/geekpi)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://leancrew.com
[b]: https://github.com/lujun9972
[1]: https://leancrew.com/all-this/2019/02/automation-evolution/
[2]: https://leancrew.com/all-this/images2019/20190223-Mistaken%20BBEdit%20replacement%20pattern.png (Mistaken BBEdit replacement pattern)
[3]: https://leancrew.com/all-this/images2019/20190223-Two-digit%20BBEdit%20replacement%20pattern.png (Two-digit BBEdit replacement pattern)
[4]: https://leancrew.com/all-this/images2019/20190223-Named%20BBEdit%20replacement%20pattern.png (Named BBEdit replacement pattern)
[5]: https://merch.barebones.com/
[6]: https://leancrew.com/all-this/images2019/20190223-BBEdit%20regex%20manual%20excerpt.png (BBEdit regex manual excerpt)