grep filename [星号]返回意外结果 [英] grep filename[asterisk] returns unexpected result

问题描述

我对ls命令有一个基本问题. 假设在一个目录中，我有4个名为

I have a basic question about ls command. Suppose in a directory I have 4 files named

run
run1
running
run.sh

所以，如果我这样做:ls -l|grep run*，那么我什么都没有.

So, if i do: ls -l|grep run* then I get no result.

但是，如果我执行ls -l|grep run.*，那么结果就是run.sh.

But if i do ls -l|grep run.* then I get run.sh as a result.

但是我希望grep列出这两种情况下的所有文件. 你能让我了解幕后发生的事情吗?

However I expected grep to list all of the files in both the cases. Could you make me understand what is going on behind scenes?

推荐答案

据我了解，"*"在执行命令本身之前已由外壳扩展，因此您的grep将尝试使用所有文件名！另一方面，grep期望使用正则表达式，因此不会按预期方式解释"*".

As long as I understand, the "*" is expanded by the shell before executing the command itself, so your grep will try to catch a string with all the file names! On the other hand, grep expects a regular expression, so the "*" is not interpreted as you expect.

直接的解决方案是:

$ ls -l run*

或者，如果您想使用grep，请在"*"后面加上正则表达式:

Or, if you want to use grep, then scape the "*" and provide a regular expression:

$ ls -l|grep run.\*
$ ls -l|grep 'run.*'

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