在 grep 中使用星号 [英] Using the star sign in grep

问题描述

我正在尝试在 linux/bash 的特定文件中搜索子字符串abc"

I am trying to search for the substring "abc" in a specific file in linux/bash

所以我这样做:

grep '*abc*' myFile

它什么都不返回.

但如果我这样做:

grep 'abc' myFile

它正确返回匹配项.

现在，这对我来说不是问题.但是如果我想 grep 一个更复杂的字符串怎么办，比如

Now, this is not a problem for me. But what if I want to grep for a more complex string, say

*abc * def *

我将如何使用 grep 完成它?

How would I accomplish it using grep?

推荐答案

星号只是一个重复运算符，但你需要告诉它你重复了什么./*abc*/ 匹配包含 ab 和零个或多个 c 的字符串(因为第二个 * 在 c 上；第一个没有意义，因为它没有任何重复).如果你想匹配任何东西，你需要说 .* -- 点表示任何字符 (在某些指导方针内).如果你只想匹配 abc，你可以说 grep 'abc' myFile.对于更复杂的匹配，您需要使用 .* -- grep 'abc.*def' myFile 将匹配包含 abc 后跟 def 的字符串以及可选的内容之间.

The asterisk is just a repetition operator, but you need to tell it what you repeat. /*abc*/ matches a string containing ab and zero or more c's (because the second * is on the c; the first is meaningless because there's nothing for it to repeat). If you want to match anything, you need to say .* -- the dot means any character (within certain guidelines). If you want to just match abc, you could just say grep 'abc' myFile. For your more complex match, you need to use .* -- grep 'abc.*def' myFile will match a string that contains abc followed by def with something optionally in between.

根据评论更新:

* 与控制台中的 * 并不完全相同.在控制台中，* 是 glob 结构 的一部分，仅用作通配符(例如 ls *.log 将列出所有以 .log 结尾的文件).但是，在正则表达式中，* 是一个修饰符，这意味着它只适用于它前面的字符或组.如果想让正则表达式中的 * 充当通配符，则需要使用前面提到的 .* -- 点是通配符，星号在修改点时表示找到一个或更多点；IE.找到一个或多个任意字符.

* in a regular expression is not exactly the same as * in the console. In the console, * is part of a glob construct, and just acts as a wildcard (for instance ls *.log will list all files that end in .log). However, in regular expressions, * is a modifier, meaning that it only applies to the character or group preceding it. If you want * in regular expressions to act as a wildcard, you need to use .* as previously mentioned -- the dot is a wildcard character, and the star, when modifying the dot, means find one or more dot; ie. find one or more of any character.

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