Linux Advanced Bash Programming (functions and summaries)

The definition format of the 1:bash function

[Function] funname [()]{action; [return int;]}

Description

1: Can be defined with function fun () or directly fun (), without any parameters.

2: The function returns a value that can be returned with a return, or, if not, the result of the execution of the last line of the function body as the return value. Return followed by a value of 0-255. After calling the function, the return value is obtained by $?

3: Parameter pass, call function, can pass parameter inside, $n ($1,$2 ...) Gets the parameter value.

2: Practical Practice

Design a function to implement the addition operation.    #!/bin/bashfunwithreturn () {echo "a+b=?" Echo-n "A=" read a echo-n "b=" read B echo-n "$a + $b =" return $ (($a + $b)} #函数调用funWithReturn # get function Execution result return value EC Ho "$?" Script execution: [[email protected] shell]$ Bash add.sha+b=?a=3b=43+4=7 Note: the addition of two variables is implemented here: $ (($a + $b)), $[a+b], ' expr $a + $b ', or $ ( Expr $a + $b)

3.bash Programming Review

Special variables:
$: script name. This variable contains the address, and you can use basename $ to get the script name.
$: First parameter
$2,$3,$4,$5,... One analogy.
$# the number of arguments passed to the script
$* displays all parameters passed to the script as a single string, to ("$ ...")
$$ the ID number of the script run
$! ID number of the last process running in the background
[Email protected] is the same as $*, but is used with quotation marks and returns each parameter in quotation marks. ("$" "$" ...)
$-Displays the current options used by the shell.
$? Displays the launch status of the last command. 0 indicates no error.

logical operators

Corresponding operation integer string
Same-eq =
Different-ne! =
Greater than-GT >
Less than-lt <
Greater than or equal to-ge
Less than or equal to-le
is empty-Z
Not empty-n

File Manipulation logical operators:
-D file----Returns True when file is a directory
-F file----Returns True when file is a normal
-R file----Returns True when file is a read-only
-S file----returns True when the files length is greater than 0 o'clock
-W file----returns True when file is a writable
-X "/bin/ls"----when/bin/ls is an executable file, returns True if the directory is accessible
-E file----Returns True when file exists
-O file----Returns True when the file owner is the current user
-Z File----Returns True when file length is 0 o'clock
-U-----The UID flag of the file is set
-G-----File has the same group ID as the current user
File1-nt file2-----file file1 than file2 update
File1-ot file2-----file file1 older than file2

4:bash Commissioning

It's hard to make mistakes during programming, and sometimes it takes more time to debug a program than to write a program, as is the case with shell programs.

The shell program is debugged primarily by using the Bash command to interpret the program's selections.
The form of calling bash is:
Bash-Select the shell program file name a few common selections are:
-e If a command fails, exit immediately.
-N reads commands but does not execute them.
-U permutation considers an undefined variable as an error.
-V displays them when they are read into the shell input lines.
-X displays commands and their arguments when the command is executed.

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Linux Advanced Bash Programming (functions and summaries)