Shell_ 07_ Functions and regular expressions

function

function ： Script code block , You can call... From anywhere by function name

1） Functions are divided into function library functions and user-defined functions , And the function name is unique ;

2） The function to be called must be created ;

3） When the function is finished , Will return a status code

// Select the return status code or return Specified value of the command

Custom function

function： Create functions in the script file

Command format ：

function  Function name （）{
    
     Procedures section 
}

（1）retun The command can end the function in advance , And return the specified status code

1） The range of directly specified values is ：0~255（ If more than 255, Then find the remainder 256）

（2） The default variable for each function is ：

1）$0 Represents the function name

2）$1 Represents the first function parameter 、$2 Represents the second function parameter （ And so on ）

（3） adopt local command , You can specify local variables inside the function

1）Shell Variables created in the script , Default to global variable

（4） If the defined function is repeated , Then the latter function will overwrite the former function

Such as ： establish show123.sh The script file will one、two、three Convert to 1、2、3

1） To write show123.sh Script files

2） call show123.sh Script files

Such as ： adopt result The command returns the status code

1） To write test25.sh Script files ;

2） call test25.sh Script files

Such as ： Create local variables in functions

1） To write test31.sh Script files

2） call test31.sh Script files

Regular expressions

Pattern template （Pattern Template）： Filter the required data in the data stream through regular expressions

Regular expressions ： Operate on strings in behavioral units

1） Regular expressions are divided into ： Basic regular expressions 、 Extended regular expression

2） Different languages may lead to different results for the same regular expression

3） Regular symbols in gawk In command , It needs to be added at the beginning and end “/” Symbol

Matching is divided into ： Greedy matching （ Default ）、 Non greedy matching

1） Greedy matching ： When multiple results match successfully , Select the one with the most successful matching data ;

2） Non greedy matching ： When multiple results match successfully , Select the one with the least successful matching data ;

// Add “？” Symbol , That is, non greedy matching

POSIX Basic regular expressions （Basic Regular Expression,BRE）：

Basic regular symbols	analysis
^	meaning ： At the beginning of the line Example ： Find a line beginning with # The line of , And the output demonstration ：grep ‘^#’ test.txt
$	meaning ： At the end of the line Example ： Find a line ending with # The line of , And the output demonstration ：grep ‘#$’ test.txt
.	meaning ： There must be an arbitrary character for Example ： Find out what contains eve、eae、e e The line of , And the output （ A space is also a character ） demonstration ：grep ‘e.e’ test.txt
*	meaning ： Represents the subsequent occurrence of the previous character 0 Times and any number of times Example ： Find out what contains es、ess、essss The line of , And the output demonstration ：grep ‘ess*’ test.txt
\	meaning ： Remove the special meaning of special symbols Example ： Find out what contains ^ The line of , And the output demonstration ：grep \^ test.txt
[ ]	meaning ： Find all lines of example characters Example ： Find out what contains aay、afy、aly The line of , And the output demonstration ：grep ‘a[alf]y’ test.txt
	meaning ： Find lines within the character range Example ： Find lines with uppercase letters demonstration ：grep ‘[A-Z]’ test.txt
{ }	meaning ： lookup n To m Lines of characters in a range Example ： lookup g To d contains 2 To 5 individual o The line of , And the output demonstration ：grep ‘go\{2,5\}d’ test.txt
	meaning ： Find out what contains n Character lines Example ： lookup g To d contains 3 individual o The line of , And the output demonstration ：grep ‘go\{3\}d’ test.txt
	meaning ： Find at least n Character lines Example ： lookup g To d contains 3 individual o The above line , And the output demonstration ：grep ‘go\{3,\}d’ test.txt
[^]	meaning ： Represents not containing a character Example ： Find a file that does not contain test The line of , And the output demonstration ：grep ‘[^test]’ test.txt

POSIX Extended regular expression （Extended Regular Expression,ERE）：

Extended regular symbol	analysis
+	meaning ： Represents the subsequent occurrence of the previous character 1 Times and any number of times Example ： Find out what contains esd、essd、essssd The line of , And the output demonstration ：grep +E ‘es+d’ test.txt
?	meaning ： Represents the subsequent occurrence of the previous character 0 Secondary sum 1 Time Example ： Find out what contains gd、god The line of , And the output demonstration ：grep +E ‘go?d’ test.txt
|	meaning ： For or on behalf of Example ： Find out what contains gd or god or good The line of , And the output demonstration ：grep +E ‘gd | god | good’ test.txt
（ ）	meaning ： Represents the combination of multiple characters Example ： Find out what contains glad and good The line of , And the output demonstration ：grep +E ‘g（la | oo）d’ test.txt
（ ）+	meaning ： Represents multiple repeated combined characters Example ： Find out what contains A123123123123C The line of , And the output demonstration ：grep +E ‘A（123）+C’ test.txt