Awk from entry to penetration (6) regular matching

awk Of pattern In addition to using simple conditional expressions , You can also use regular expressions .

AWK Regular expressions can be processed easily and efficiently . A large number of complex tasks can be solved by extremely simple regular expressions . Everyone who is proficient in the command line knows the real power of regular expressions .

This chapter will focus on the use of standard regular expressions .awk The regularity of is basically the same as that of ordinary regularity , But in awk You need to use two regular expressions in / wrap up .

spot （Dot）

Dot character （.） You can match all characters except the end of line character . For example, the stool below can match fin, fun, fan wait .

$ echo -e "cat\nbat\nfun\nfin\nfan" | awk '/f.n/'

Executing the above command can get the following results ：

fun
fin
fan

OK, let's start

Line start (^) Match the beginning of a line . The following example will output all the characters as strings The The first line .

$ echo -e "This\nThat\nThere\nTheir\nthese" | awk '/^The/'

You can get the following result by executing the above command ：

There
Their

End of line

Line end ($) Match the end of a line . In the following example, all characters will be output n The ending line ：

$ echo -e "knife\nknow\nfun\nfin\nfan\nnine" | awk '/n$/'

You can get the following result by executing the above command ：

Ca
fin
fan

Match character set

Matching character sets are used to match sets （ Denoted by square brackets ） A character in . In the following example , matching Call And Tall It doesn't match Ball.

$ echo -e "Call\nTall\nBall" | awk '/[CT]all/'

You can get the following result by executing the above command ：

Call
Tall

Exclusion set

Regular matching excludes characters from the set . In the following example, only Ball.

$ echo -e "Call\nTall\nBall" | awk '/[^CT]all/'

You can get the following result by executing the above command ：

Ball

or

A vertical bar (|) Allow regular expressions to implement logic or operations . The following example will output Ball And Call .

$ echo -e "Call\nTall\nBall\nSmall\nShall" | awk '/Call|Ball/'

You can get the following result by executing the above command ：

Call
Ball

Once at most

The symbol ( ？) The preceding character does not appear or appears once . The following example matches Colour And Color. Use ? bring u Becomes an optional character .

$ echo -e "Colour\nColor" | awk '/Colou?r/'

You can get the following result by executing the above command ：

Colour
Color

Zero or more times

The symbol (＊) Allow the character before it to appear multiple times or not . The following example will match ca,cat, catt wait .

$ echo -e "ca\ncat\ncatt" | awk '/cat*/'

You can get the following result by executing the above command ：

ca
cat
catt

One or more times

The symbol (+) Make the character before it appear one or more times . The following example will match a 2 Or multiple consecutive 2.

$ echo -e "111\n22\n123\n234\n456\n222"  | awk '/2+/'

You can get the following result by executing the above command ：

22
123
234
222

grouping

Brackets are used for grouping and characters | Used to provide a variety of options . The following regular expression will match all that contain Apple Juice or Aplle Cake The line of .

$ echo -e "Apple Juice\nApple Pie\nApple Tart\nApple Cake" | awk '/Apple (Juice|Cake)/'

You can get the following result by executing the above command ：

Apple Juice
Apple Cake

Multiple expressions can use && perhaps , come together , The meaning of and :

awk ‘/^ Start time date /,/^ End time date /’ nginx.log
 such as , Query time period 2021-03-24 10:12:12  To  2021-09-24 10:12:12,
 It can be used awk ‘/^2021-03-24 10:12:*/,/^2021-09-24 10:12:*/’ nginx.log Inquire about .