正则表达式

Regular Expression（正则表达式）
模式配对，判断一个字符串能否满足配对规则

awk中的正则表达式写在两个//中间
awk '/a.c/{print $0}' data.txt 
awk '/abc/{print $0}' data.txt 
awk '/^abc/{print $0}' data.txt 
awk '/$abc/{print $0}' data.txt 

1./abc/

"abc"
"xxabcl"
"xxabcxx1"
"a bc"    //不符合要求

2./a.c/ //.表示单一字符

"abc"
"aac"
"acc"
"adc"
"aec"
"a c"

3.转义字符来背锅

/a\.c/
"a.c"

/a\/c/
"a/c"

/a\\c/
"a\c"

/a\?c/
"a?c"

4.^和$

/^abc/
"abc"
"abcxxx"
"abcxxxx1"
"abc..."
"xabc"         X
"Aabc"          X

/abc$/
"abc"
"xxxabc"
"xxxxabc"
"abcxxx"          X

5.[] 表示或

/a[xyz]c/
"axc"
"ayc"
"azc"
"axyc"               X

/a[a-z]c/
"aac"
"abc"
"acc"
"adc"
"aAc"               X

/a[a-zA-Z]c/
"aac"
"aAc"
"Aaac"

/a[^a-z]c/  表示不是a-c中的一个字符
"aac"                  X
"aAc"                X

6.*和+

/a*b/  *之前的字符可以出现任意次数
"b1"
"ab"
"aab"
"aaab"
"aaaaaaab"

/a+b/  +前的字符至少出现一次
"ab"
"aab"
"aaab"
"aaaab"
"b"                         X

7.?

/a?b/
"b1""ab"

8.{}

/ab{3}c/
"abbbc"

/ab{3,4}c/
"abbbc"
"abbbbc"
"abbbbbc"                         X
/ab{3,10}c/    b出现的次数从3到10次都可以
/ab{3,}c/    至少出现三个b
"abbbbbbbbdc"           X 多了一个d

9.() 括号括起来的要反复出现

/(ab)+c/
"abababababc"
"abc"
"ababc"
"abbc"             X