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Regex 正規表示式

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Awk

測試 Regex 語法

 (awk)
# echo "Testing regex using awk" | awk '/regex/{print $0}'
Testing regex using awk

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

# echo "likegeeks website" | awk '/^likegeeks/{print $0}'
likegeeks website

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}'
Operators
 Description
[abc]
 Match any single character from from the listed characters
[a-z]
 Match any single character from the range of characters
[^abc]
 Match any single character not among listed characters
[^a-z]
 Match any single character not among listed range of characters
.
 Match any single character except a newline
\
 Turn off (escape) the special meaning of a metacharacter
^
 Match the beginning of a line.
$
 Match the end of a line.
*
 Match zero or more instances of the preceding character or regex.
?
 Match zero or one instance of the preceding character or regex.
+
 Match one or more instances of the preceding character or regex.
{n,m} Match a range of occurrences (at least n, no more than m) of preceding character of regex.
|
 Match the character or expression to the left or right of the vertical bar.

數字字元:

  • [[:digit:]]* : any number of digits (zero or more)
  • [[:digit:]]+ : at least one digit
  • [[:digit:]]? : zero or one digits
  • [[:digit:]]{1,3} : at least one and no more than three digits
  • [[:digit:]]{2,} : two or more digits

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
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