Linux Control Structure

Linux control structure-general Linux technology-Linux programming and kernel information. The following is a detailed description. Ignore the referenced value in double quotes in Linux, except $ '\.

Ignore all referenced values in single quotes

For example, echo '$ Test'

$ Test

Reverse quotation marks: Use the content as a command

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Condition test: 0 true, 1 false

Test condition or [condition]

1) file [-w 1.txt? O? R 2.txt]

2) string [$ EDITOR = "vi"] = ,! =,-Z,-n

3) value [$ number? Eq "12"]? Eq,-ne,-gt,-lt,-le,-ge

4) Loop = 'expr $ loop + 1' let x = $ x + 1

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1) If ["10 "? Lt "12"]; then

Echo "yes"

Fi

If [-t] test whether the interactive mode is used

Empty command: elif else

2) for loop in 1 2 3 4 5 (list such as 'LS ')

Do

Echo"

Done

3) while [$ counter lt "5"]

Do

Echo ""

Done

Other break and continue

Case,

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Number of parameters $ #, parameter $ @, exit Status $?

[Function] message ()

{...

}

Message "hello" "world"

Parameter: $1, $2 ,...... $9

It retains the current s h e l and memory information. In addition, if you execute or call another piece of code in a script file, a separate s h e l will be created, thus removing all existing variables defined in the original script.

Once the file is loaded into s h e l, you can call the function in the command line or script. You can use the s e t command to view all definitions.

. The output list contains all functions loaded into s h e l.

To change the function, run the u n s e t command to delete the function from s h e l, even though u n s e t deletes the function to facilitate this function.

Numbers are not available for s h e l or scripts, but they are not actually deleted. After the modification, re-load the file. Some s h e l will identify the changes and do not need to use the u n s e t command, but for security reasons, it is best to use the u n s e t command when changing the function.

Unset function_name

Locate function files

./Path
Source path