Shell function, system function, basename [string / pathname] [suffix] can be understood as taking the file name in the path, dirname file absolute path, and user-defined function

1. function

1.1 System function

1.1.1basename

1.1.1.1 Basic grammar

basename [string / pathname] [suffix] （ Function description ：basename The command will delete all prefixes including the last （‘/’） character , Then display the string .
basename It can be understood as taking the file name in the path
Options ：
suffix For the suffix , If suffix Designated ,basename Will pathname or string Medium suffix Get rid of .

1.1.2dirname

dirname File absolute path （ Function description ： Remove filename from given filename with absolute path （ Non catalog part ）, Then return to the rest of the path （ Part of the catalog ））
dirname It can be understood as the absolute path name of the file path

1.1.3 Case study

1.1.3.1date+%s Timestamp exercise

1.1.3.2basename The practice of

Cut out the file name

parameter File code

The displayed file name includes the path , We don't need the output path , So add basename To solve

1.1.3.3dirname The practice of

dirname Intercept the path before the last slash , Do not include filename
and basename Intercept the file name after the last slash , Exclude path

If only pwd Words , Executing code in other folders will not print the directory of the script , Need to add dirname, as follows

add dirname The script path after output remains unchanged

1.2 Custom function

1.2.1 Basic grammar

[ function ] funname[()] 
{
     
	Action; 
	[return int;] 
}

1.2.2 Experience and skill

（1） Must be before calling function place , Declare function first ,shell The script is run line by line . It doesn't compile first like any other language .
（2） Function return value , Only through $? System variable acquisition , Can display plus ：return return , If not , Results will be run with the last command , As return value .return Heel value n(0-255)

1.2.3 Case study

1.2.3.1 Not used return Version of

Can output and

1.2.3.2 use return If you come back

It can be seen that ,return It must be followed by a number , Revised as follows ：

In this way, the results can be output normally , however return Can only return 0-255, If the number exceeds, the correct answer cannot be displayed , as follows

156+245！=145 Of , So it can explain return Only return 0-255 Number of numbers , How can we solve this problem , Look at the code below

In this way, the function add Inside echo The value is assigned to ans, And then output

The result is also right , Explain that this is correct