为什么在grepping ps时，在正则表达式中用括号括起来的单个字符会排除grep本身？ [英] Why does enclosing a single char in brackets in a regex exclude the grep itself when grepping ps?

问题描述

  $ ps -ef |如果我在Linux机器上执行以下grep： grep bash 
 root 2286 1 0 Jun06？ 00:03:15 / bin / bash /etc/init.d/zxy100wd 
 wmiller 6436 6429 0 Jun06 pts / 0 00:00:01 bash 
 wmiller 10707 6429 0 Jun07 pts / 1 00:00 ：00 bash 
 wmiller 10795 6429 0 Jun07 pts / 2 00:00:00 bash 
 wmiller 16220 6436 0 06:55 pts / 0 00:00:00 grep --color = auto bash 
  

请注意，最后一行报告的是grep本身，因为单词bash在参数grep中。

  $ b 
 code> $ ps -ef | grep ba [s] h 
 root 2286 1 0 Jun06？ 00:03:15 / bin / bash /etc/init.d/zxy100wd 
 wmiller 6436 6429 0 Jun06 pts / 0 00:00:01 bash 
 wmiller 10707 6429 0 Jun07 pts / 1 00:00 ：00 bash 
 wmiller 10795 6429 0 Jun07 pts / 2 00:00:00 bash 
  

没有关于grep的信息！

那么，为什么在搜索词中加入一个字母，即括号里的正则表达式，让grep不能在这里报告呢？我虽然[s]的意思是由字符s组成的[]中的任何字符。

解决方案

因为表达式 ba [s] h （或 [b] ash 或...）只是匹配 bash ，而不是 ba [s] h （或 [b] ash 或$）。

因此， grep 命令正在寻找所有包含 bash ：

  root 2286 1 0 Jun06？00:03:15 / bin / bash /etc/init.d/zxy100wd 
 wmiller 6436 6429 0 Jun06 pts / 0 00:00:01 bash 
 wmiller 10707 6429 0 Jun07 pts / 1 00:00:00 bash 
 wmiller 10795 6429 0 Jun07 pts / 2 00:00:00 bash 
  

但是

  wmiller 16220 6436 0 06:55 pts / 0 00:00:00 grep --color = auto ba [s] h 
  

不匹配，因为它不完全是 bash 。

If I perform the following grep on my Linux box:

$ ps -ef | grep bash
root      2286     1  0 Jun06 ?        00:03:15 /bin/bash /etc/init.d/zxy100wd
wmiller   6436  6429  0 Jun06 pts/0    00:00:01 bash
wmiller  10707  6429  0 Jun07 pts/1    00:00:00 bash
wmiller  10795  6429  0 Jun07 pts/2    00:00:00 bash
wmiller  16220  6436  0 06:55 pts/0    00:00:00 grep --color=auto bash

Note the last line is reporting the grep itself because the word "bash" is in the args to grep.

But, if instead I put [] around any letter in "bash" I get:

$ ps -ef | grep ba[s]h
root      2286     1  0 Jun06 ?        00:03:15 /bin/bash /etc/init.d/zxy100wd
wmiller   6436  6429  0 Jun06 pts/0    00:00:01 bash
wmiller  10707  6429  0 Jun07 pts/1    00:00:00 bash
wmiller  10795  6429  0 Jun07 pts/2    00:00:00 bash

No info on the grep this time!

So, why does enclosing a letter in the search term, i.e. the regex, in brackets keep grep from reporting itself here? I though [s] meant "any character from the [] enclosed set consisting of the character "s".

解决方案

This is because the expression ba[s]h (or [b]ash, or...) just matches bash, not ba[s]h (or [b]ash, or...).

So the grep command is looking for all lines with bash:

root      2286     1  0 Jun06 ?        00:03:15 /bin/bash /etc/init.d/zxy100wd
wmiller   6436  6429  0 Jun06 pts/0    00:00:01 bash
wmiller  10707  6429  0 Jun07 pts/1    00:00:00 bash
wmiller  10795  6429  0 Jun07 pts/2    00:00:00 bash

but

wmiller  16220  6436  0 06:55 pts/0    00:00:00 grep --color=auto ba[s]h

does not match because it is not exactly bash.

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