grep
基本语法：grep [选项] [--color=auto] “搜索的字符串” filename
-
-A：后面接数字，为after的意思。除了列出该行，后续的n行也列出来 -
-B：与-A相反，列出前面的n行 -
-v：不包含[搜索的字符串]的行都列出来 -
-n：显示行号 -
-i：无视字母大小写
案例
准备数据
"Open Source" is a good mechanism to develop programs.
apple is my favorite food.
Football game is not use feet only.
this dress doesn't fit me.
However, this dress is about $ 3183 dollars.^M
GNU is free air not free beer.^M
Her hair is very beauty.^M
I can't finish the test.^M
Oh! The soup taste good.^M
motorcycle is cheap than car.
This window is clear.
the symbol '*' is represented as start.
Oh!
My god!
The gd software is a library for drafting programs.^M
You are the best is mean you are the no. 1.
The world <Happy> is the same with "glad".
www.linuxidc.com I like dog.
google is the best tools for search keyword.
goooooogle yes!
go! go! Let's go.
查找特定字符串
# 搜索特定字符串
grep -n "the" regular_express.txt
# 反向选择
grep -nv "the" regular_express.txt
# 不区分大小写
grep -in "the" regular_express.txt
利用[]查找集合字符
# 1
grep -n "t[ae]st" regular_express.txt
# 2
grep -n "oo" regular_express.txt
# 3,不让「oo」前有「g」
grep -n "[^g]oo" regular_express.txt
# 4，不让「oo」前有「小写字母」
grep -n "[^a-z]oo" regular_express.txt
行首和行尾字符^$
# the在行首
grep -n "^the" regular_express.txt
# 行首是小写字母
grep -n "^[a-z]" regular_express.txt
# 以「.」结尾的
grep -n "\.$" regular_express.txt
# 找出空白行
grep -n "^$" regular_express.txt
# 非空白行
grep -nv "^$" regular_express.txt
注意：^符号在[]内外是不同的，括号内表示「反向选择」，括号外表示「行首」
任意一个字符和重复字符.;*
-
.：一定有一个任意字符 -
*：0到无穷多个前一个字符 -
.*：任意字符
案例
# 1
grep -n "g..d" regular_express.txt
# 2，注意：此处代表至少有2个o
grep -n "ooo*" regular_express.txt
# ，如果我想要字符串开头与结尾都是 g，但是两个g之间仅能存在至少一个o，亦即是 gog, goog, gooog.... 等等
grep -n "goo*g" regular_express.txt
# 找出g开头与g结尾的字符串，当中的字符可有可无
grep -n "g.*g" regular_express.txt
注意：g*代表「空字符或者一个和一个以上的g」；那么g*g就代表「g,gg,ggg等」
限定连续字符范围{}
注意：使用{}的时候需要加上转义符
# 两个「o」的字符串
grep -n "o\{2\}" regular_express.txt
# 「g」后面接2-5个「o」，然后再接「g」
grep -n "go\{2,5\}g" regular_express.txt
# 2 个o 以上的 goooo....g
grep -n "gooo*" regular_express.txt
grep -n "go\{2,5\}" regular_express.txt
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