问题描述
如果我在我的 Linux 机器上执行以下 grep:
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
请注意，最后一行是报告 grep 本身，因为bash"一词在 grep 的参数中.
Note the last line is reporting the grep itself because the word "bash" is in the args to grep.
但是，如果我将 [] 放在 "bash" 中的任何字母周围，我会得到:
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
这次没有关于 grep 的信息！
No info on the grep this time!
那么，为什么将搜索词中的字母(即正则表达式)括在括号中会阻止 grep 在这里报告自己?我虽然 [s] 的意思是[] 封闭集合中的任何字符，由字符s"组成.
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".
推荐答案
这是因为表达式 ba[s]h (or [b]ash, or...) 只匹配bash，而不是ba[s]h(或[b]ash，或...).
This is because the expression ba[s]h (or [b]ash, or...) just matches bash, not ba[s]h (or [b]ash, or...).
所以 grep 命令正在寻找所有带有 bash 的行:
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
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.
does not match because it is not exactly bash.
这篇关于为什么在对 ps 进行 grepping 时，将单个字符括在正则表达式中的括号中会排除 grep 本身?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！