正規表示式-Regex

基本搜尋

// 搜尋字串區分大小寫
$ echo "This is a test" | sed -n '/test/p'

$ echo "This is a test" | awk '/test/{print $0}'

// 可以包含空白與數字
$ echo "This is a test 2 again" | awk '/test 2/{print $0}' 

特殊字元

字元：.*[]^${}\+?|()

$ cat myfile
There is 10$ on my pocket

$ awk '/\$/{print $0}' myfile

$ echo "\ is a special character" | awk '/\\/{print $0}' 

$ echo "This ^ is a test" | sed -n '/s ^/p'

搜尋字首與字尾

// 搜尋字首
$ echo "likegeeks website" | awk '/^likegeeks/{print $0}'

// 搜尋字尾
$ echo "This is a test" | awk '/test$/{print $0}' 

// 搜尋相同字元行的文字
$ awk '/^this is a test$/{print $0}' myfile

// 不顯示空白行
$ awk '!/^$/{print $0}' myfile

搜尋字元

用 dot

# cat myfile
this is a test
This is another test
And this is one more
start with this

# awk '/.st/{print $0}' myfile
this is a test
This is another test

用 [ ]

// 包含 oth 與 ith
# awk '/[oi]th/{print $0}' myfile
This is another test
start with this

// 不包含 oth 與 ith
# awk '/[^oi]th/{print $0}' myfile
And this is one more
start with this                  <== 有兩個 th

使用範圍

# awk '/[e-p]st/{print $0}' myfile
this is a test
This is another test

$ echo "123" | awk '/[0-9][0-9][0-9]/'

# awk '/[a-fm-z]st/{print $0}' myfile
this is a test
This is another test