Shell knowledge point supplement (5)-case. In. esac/function/while done/until done

1. case... in... esac

The syntax of case... in... esac is as follows:
Case $ variable name in
"First variable content ")
Program Section
;;
"Second variable content ")
Program Section
;;
*)
Other Program Execution segments that do not contain the first variable content or the second variable content
Exit 1
;;
Esac
Note that this syntax starts with case and ends with esac,

Write a program: allows the user to enter one, two, three, and display the user's variables on the screen. If it is not one, two, three, only these three options are available.
[Root @ Linux Scripts] # vi sh11.sh
#! /Bin/bash
# Program:
# Let user input one, two, three and show in screen.
# History:
#2005/08/29 vbird first release
Path =/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin :~ /Bin
Export path
Echo "this program will print your selection! "
# Read-P "input your choice:" Choice
# Case $ choice in
Case $1 in
"One ")
Echo "your choice is one"
;;
"Two ")
Echo "your choice is two"
;;
"Three ")
Echo "your choice is three"
;;
*)
Echo "usage {one | two | three }"
;;
Esac
In this case, you can run the "Sh sh11.sh two" command to receive the corresponding response. The above method is directly issued. If interactive mode is used, remove the "#" of the 10th and 11 rows above and add the 12 rows with comments (#)

Practice:

1 #! /Bin/bash
2
3
4 echo "practice to use" one "" two "" three ""
5 read-P "input your choise (from the up suggest):" answer
6
7 case "$ answer" in
8 "one ")
9 echo "your input is 'one', that is $ answer"
10 ;;
11 "two ")
12 echo "your input is 'two', that is $ answer"
13 ;;
14 "three ")
15 echo "your input is 'three ', that is $ answer"
16 ;;
17 *)
18 echo "$ answer is wrong, {you only have the hinted three choices }"
19 ;;
20 esac

LOONG:/home/Yee/shell # sh case_practise.sh
Practice to use one two three
Input your choise (from the up suggest): One
Your input is 'one', that is one
LOONG:/home/Yee/shell # sh case_practise.sh
Practice to use one two three
Input your choise (from the up suggest): Two
Your input is 'two', that is two
LOONG:/home/Yee/shell # sh case_practise.sh
Practice to use one two three
Input your choise (from the up suggest): Three
Your input is 'three ', that is three
LOONG:/home/Yee/shell # sh case_practise.sh
Practice to use one two three
Input your choise (from the up suggest): xxxx
XXXX is wrong, {you only have the hinted three choices}
LOONG:/home/Yee/shell #

2. Function

Function also has built-in variables ~ His built-in variables are similar to shell scripts. The function name represents $0, and the subsequent variables are replaced by $1, $2 ~ It's easy to make a mistake here ~ Because $0, $1... in "function fname () {program segment}" is different from $0 in shell script. For the sh11-2.sh above, if I say "Sh sh11-2.sh one", this indicates that $1 in shell script is the string "one. But in printit ()
The $1 in is irrelevant to this one. Let's rewrite the above example to make it clearer!
# Vi sh11-3.sh [root @ Linux Scripts] #
#! /Bin/bash
# Program:
# Let user input one, two, three and show in screen.
# History:
#2005/08/29 vbird first release
Path =/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin :~ /Bin
Export path
Function printit (){
Echo "your choice is $1"
}
Echo "this program will print your selection! "
Case $1 in
"One ")
Printit 1
;;
"Two ")
Printit 2
;;
"Three ")
Printit 3
;;
*)
Echo "usage {one | two | three }"
;;
Esac
In the above example, if you enter "Sh sh11-3.sh one", the word "your choice is 1" will appear ~ Why is it 1? In the program section, if we write "printit 1", that 1 will become $1 in the function.

3. While done/until done

While do done, until do done
In general, the most common loop is the following two states:
While [condition]
Do
Procedure Section
Done
In this method, while is "when .... therefore, this method refers to the meaning of "when the condition is set, a loop is executed until the condition of the condition is not set.
Until [condition]
Do
Procedure Section
Done
This method is the opposite of while. It says, "when the condition is set, the loop is terminated; otherwise, the loop continues .』

What if I want to calculate the data of 1 + 2 + 3 +... + 100? Use Loops ~ He is like this:
[Root @ Linux Scripts] # vi sh13.sh
#! /Bin/bash
# Program:
# Try to use loop to calculate the result "1 + 2 + 3... + 100"
# History:
#2005/08/29 vbird first release
Path =/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin :~ /Bin
Export path
S = 0
I = 0
While ["$ I "! = "100"]
Do
I = $ ($ I + 1 ))
S = $ ($ S + $ I ))
Done
Echo "the result of '1 + 2 + 3 +... + 100 'is => $ S"
Hey! After you run "Sh sh13.sh", you can get 5050 of the data! So you can call ~ So let's do it by yourself. If you want the user to enter a number and set the program to 1 + 2 +... until the number you entered, how can you write it?

Practice:

Version 1: While done

1 #! /Bin/bash
2
3 read-P "Please input the stop number:" Input
4 S = 0
5 I = 0
6 While ["$ I "! = "$ Input"]
7 do
8 I =$ ($ I + 1); # echo "I = $ I"
9 S = $ ($ S + $ I); # echo "s = $ S"
10 done
11 echo "the result is: $ S"

LOONG:/home/Yee/shell # sh self_add.sh
Please input the stop number: 100
The result is: 5050
LOONG:/home/Yee/shell #

Version 2: until done

1 #! /Bin/bash
2
3 read-P "Please input the stop number:" Input
4 S = 0
5 I = 0
6 Until ["$ I" =
"$ Input"] # You only need to modify it in two places.
7 do
8 I =$ ($ I + 1); # echo "I = $ I"
9 S = $ ($ S + $ I); # echo "s = $ S"
10 done
11 echo "the result is: $ S"
~
Please input the stop number: 50
The result is: 1275
LOONG:/home/Yee/shell # sh self_add2.sh
Please input the stop number: 100
The result is: 5050
LOONG:/home/Yee/shell # sh self_add2.sh
Please input the stop number: 4
The result is: 10
LOONG:/home/Yee/shell #

4. For... do... Done

The for syntax is in the state of "know how many cycles are required! His syntax is:
For (initial value; Restriction value; execution step ))
Do
Program Section
Done
This syntax is suitable for numeric calculation. The content of the three strings following the for clause indicates:
• Initial Value: the initial value of a variable in the loop, which is directly set with a variable similar to I = 1;
• Limit Value: when the value of a variable is within the limit value range, the loop continues. For example, I <= 100;
• Execution step: the amount of variable changes during each cycle. For example, I = I + 1.
It is worth noting that, in the "execution step" setting, if you add 1 at a time, you can use a method similar to "I ++, that is to say, I adds one to each loop. Okay. Let's use this method to accumulate 1 to 100!
[Root @ Linux Scripts] # vi sh14.sh
#! /Bin/bash
# Program:
# Try do calculate 1 + 2 +... + 100
# History:
#2005/08/29 vbird first release
Path =/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin :~ /Bin
Export path
S = 0
For (I = 1; I <= 100; I = I + 1 ))
Do
S = $ ($ S + $ I ))
Done
Echo "the result of '1 + 2 + 3 +... + 100 'is => $ S"

You can also use the following method to perform non-digital operations!
For VaR in con1 con2 con3...
Do
Program Section
Done
In the preceding example, when the $ var variable content cyclically works:
1. During the first loop, the content of $ VaR is con1;
2. For the second loop, the content of $ VaR is con2;
3. For the third loop, the content of $ VaR is con3;
4 .....
We can make a simple exercise. Suppose I have three animals: dog, cat, and elephant. If I want to output the following words in each row: "There are dogs...", you can:
[Root @ Linux Scripts] # vi sh15.sh
#! /Bin/bash
# Program:
# Using for... loop to print 3 animal
# History:
#2005/08/29 vbird first release
Path =/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin :~ /Bin
Export path
For animal in Dog Cat elephant
Do
Echo "there are" "$ animal" "s ...."
Done

In addition, you can test the directory in sequence as follows:

Filelist = 'ls $ dir'
For filename in $ filelist
Do
Perm = ""
Test-R "$ DIR/$ FILENAME" & perm = "$ perm readable"
Test-W "$ DIR/$ FILENAME" & perm = "$ perm writable"
Test-X "$ DIR/$ FILENAME" & perm = "$ perm executable"
Echo "the file $ DIR/$ filename's permission is $ perm"
Done

5. shell script tracing and debugging

[Root @ Linux ~] # Sh [-nvx] scripts. Sh
Parameters:
-N: do not execute the script. Only query the syntax;
-V: Before executing scloud, output the content of scripts to the screen;
-X: displays the used script content on the screen. This is a useful parameter!
Example:
Example 1: Is there a syntax problem in the test sh16.sh?
[Root @ Linux ~] # Sh-N sh16.sh
# If the syntax is correct, no information is displayed!
Example 2: list all the sh15.sh execution processes ~
[Root @ Linux ~] # Sh-x sh15.sh
+ Path =/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:/home/vbird/bin
+ Export path
+ For animal in Dog Cat elephant
+ Echo 'there are dogs ....'
There are dogs ....
+ For animal in Dog Cat elephant
+ Echo 'there are cats ....'
There are cats ....
+ For animal in Dog Cat elephant
+ Echo 'there are elephants ....'
There are elephants ....
# Using-X is really a good method for tracking scripts. It can lead all the program segments with execution,
# If it is a program section, + font size will be added at the beginning of the output, indicating that it is the program code,
# The actual output is related to standard output ~ As shown above.
In Example 2 above, we can use this simple parameter-X to achieve the debug goal. This is a rare parameter. Generally, if a problem occurs when you execute a script, with this-x parameter, you can know the row where the problem occurs!

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