Bash Script programming case statements and scripting options advanced

Case statement and scripting Options Advanced Detail

the control flow in the process-oriented programming language (that is, the statements in the program) is executed sequentially by default.

Control structure of programming language there are three categories:

1, sequential structure

2, select structure

(1) If statement

If statement for a single branch

Format: If Condition1;then

Expression

...

Fi

If statement for two branches

Format: If Condition1;then

Expression

...

Else

Expression

...

Fi

If statements for multiple branches

Format: If Condition1;then

Expression

...

Elif Condition2;then

Expression

...

Else

Expression

...

Fi

A multi-branched if statement is less efficient to perform because it is a condition that is then compared to a condition.

(2) Case statement

We choose a structure with a second statement, that is, our case statement, more explicit structure than the multi-branch if statement, simpler to use, more efficient choice of structure statements.

Usage format: case (keyword) SWITCH (variable, which refers to the value of a variable, not the variable itself) in

And the value of our variable will have the following several cases

Value 1) This is not the condition, but the value of the variable, the first value of the variable

Expression

...;;( None of the options can end with a double semicolon)

Value 2)-the second type

Expression

...;;

...

*)

Expression

...

Esac

Value can have more than one

Exercise: Write a script that asks

Let the user type the content from the keyboard and then use our script to determine what the user typed and display it

Type a number to display a number, type a lowercase letter to display lowercase letters, and type uppercase letters to show uppercase

Script content:

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M01/85/29/wKioL1ebL7mgZa3XAABDGHZIqAc834.png "title=" w~j8_) @9[zkqy$j~ccwun8k.png "alt=" Wkiol1ebl7mgza3xaabdghziqac834.png "/>

Script Execution Results:

650) this.width=650; "src=" Http://s4.51cto.com/wyfs02/M02/85/29/wKiom1ebL9DyYyrxAAAYOxuQ1eU309.png "title=" ~ Bqrl4i4em85jccfmscqz_l.png "alt=" Wkiom1ebl9dyyyrxaaayoxuq1eu309.png "/>

Exercise: Write a script that asks

The script only receives one of these four parameters, Start,stop,restart,status

And then display the corresponding content

Script content:

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M00/85/29/wKiom1ebMSjzu5f2AABBnY3g95Q535.png "title=" O) q}l~ FS6) @ @Z88SLD) egpy.png "alt=" Wkiom1ebmsjzu5f2aabbny3g95q535.png "/>

Script Execution Results:

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M02/85/29/wKioL1ebMTfSZDldAAAzU435f20579.png "title=" R61ale }P_4O6T) 6z97hkn (f.png "alt=" Wkiol1ebmtfszdldaaazu435f20579.png "/>

Exercise: Write a script that asks

Can receive the options and parameters, and then get each option and parameters, and can be based on options and parameters to make a specific operation

Like->boke3.sh--add tom,jerry--del tom,blair-v|--verbose-h|--help

Script content:

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M00/85/29/wKioL1ebOMDBbETdAACzvXN7gOs555.png "title=" _ 4zzfvuimwm~q}bd@r ' {z9m.png ' alt= "Wkiol1ebomdbbetdaaczvxn7gos555.png"/>

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M01/85/29/wKiom1ebONmQg6HYAACLVWZ0Bpg884.png "title=" Rg{_ " am{_tyk1t@51wl[' Km.png "alt=" Wkiom1ebonmqg6hyaaclvwz0bpg884.png "/>

Script Execution Results:

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M01/85/29/wKioL1ebOPOTrJBxAAAzCFpQTGg367.png "title=" C%g_ 1lf~p}6$}pjbhboiypk.png "alt=" Wkiol1ebopotrjbxaaazcfpqtgg367.png "/>

Exercise: Write a script that asks

The script is named boke4.sh

The script is formatted as SHOWLOGGED.SH-V-c-h|--help

Where-h option can only be used alone to display help information;

The-C option displays the number of all users logged on on the current system, and if the-v option is used at the same time, displays both the number of simultaneous users and information about the logged-on user.

Script content:

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M02/85/2A/wKioL1ebSS_BwpqtAADBo5A3jRQ420.png "title=" 9% 9D6K5SGXV_CT) ymneaiex.png "alt=" Wkiol1ebss_bwpqtaadbo5a3jrq420.png "/>

Script Execution Results:

650) this.width=650; "src=" Http://s2.51cto.com/wyfs02/M00/85/2A/wKiom1ebSUbQ4cL0AABOx9ipH24026.png "title=" vfyzu{ 1VQE '}x1]6bdvbf}a.png "alt=" Wkiom1ebsubq4cl0aabox9iph24026.png "/>

3, Cycle structure

For statement

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Bash Script programming case statements and scripting options advanced