[20210802]grep奇怪的过滤.txt

--//使用grep过滤遇到的奇怪问题.做一个记录.

$ cat a3.txt
struct ktetb[25], 8 bytes                   @308
   ub4 ktetbdba                             @308      4280320
   ub4 ktetbnbk                             @312      128
struct ktetb[26], 8 bytes                   @316
   ub4 ktetbdba                             @316      4288512
   ub4 ktetbnbk                             @320      128
aaa ^^st

--//^在正则表达式里面解析为开头.但是有点奇怪的是
$ egrep "^^^^^^^^^^st" a3.txt
struct ktetb[25], 8 bytes                   @308
struct ktetb[26], 8 bytes                   @316

$ egrep "^^st" a3.txt
struct ktetb[25], 8 bytes                   @308
struct ktetb[26], 8 bytes                   @316

$ egrep "\^\^st" a3.txt
aaa ^^st

--//egrep执行,无论前面多少^开头，都是显示行开头是st的行。要转义一下才支持显示^^st的行.而如果写成如下:

$ grep "^^st" a3.txt

--//没有输出.

$ grep "\^\^st" a3.txt
aaa ^^st

--//如果看手册:
Egrep is the same as grep -E. Fgrep is the same as grep -F.

-E, --extended-regexp
Interpret PATTERN as an extended regular expression (see below).

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[20210802]grep奇怪的过滤.txt

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