grep基本学习

参考：

《跟老男孩学Linux运维：核心系统命令实战》　

在线bash:https://c.runoob.com/compile/18

实现or,and,not:https://www.jianshu.com/p/4ec50fdaf388

 

grep：　global search regular expression(RE) and print out the line

注意学习几个参数的含义

• 不加参数，显示匹配的行，起到搜索作用

echo '   hello; world;ni; hao
chen;pan;   this
xie; juan' > test.txt
grep "o" test.txt

输出为：   hello; world;ni; hao 

• -v 显示不匹配的行，起到排除的作用

echo '   hello; world;ni; hao
chen;pan;   this
xie; juan' > test.txt
grep -v "o" test.txt

输出为：

chen;pan;   this
xie; juan 

• -n 显示匹配的行，并且加上行号，起到查询作用，当匹配内容为正则表达式"."，则会对所有行加上行号输出

echo '   hello; world;ni; hao
chen;pan;   this
xie; juan' > test.txt
grep -n "o" test.txt

输出为：

1:   hello; world;ni; hao

• -i 不区分大小写

echo '   hello; world;ni; hao
chen;pan;   this
xie; juan' > test.txt
grep -i "X" test.txt

输出为：xie; juan

• -E 使用扩展的egrep，将匹配模式延伸为正则表达式使用

echo '   hello; world;ni; hao
chen;pan;   this
xie; juan' > test.txt

grep "x\|c" test.txt
grep -E "x|c" test.txt
egrep "x|c" test.txt
grep -e "x" -e "c" test.txt

四种写法一样，结果都是：

chen;pan;   this
xie; juan

• -c 只计算匹配的行数（注意不是匹配次数）

echo '   hello; world;ni; hao
chen;pan;   this
xie; juan' > test.txt

grep -c "x\|c" test.txt

输出结果为：２

--color[=WHEN]为匹配处的字符串添加颜色，可选的为auto, always, never

echo '   hello; world;ni; hao
chen;pan;   this
xie; juan' > test.txt

grep --color=always "x\|c" test.txt

输出为：（在线bash）

[01;31m[Kc[m[Khen;pan;   this
[01;31m[Kx[m[Kie; juan

• -w 只输出含有整个单词的行

echo '   hello; world;ni; hao
chen;pan;   this
xie; juan' > test.txt

grep -w "xi" test.txt
echo "-----------"
grep -w "xie" test.txt

输出为：

-----------
xie; juan