Learning shell script programming (Issue 1) _ using variables in Shell programs

• Variable assignment
• Variable access
• Variable input

 

4.1 variable assignment

In shell programming, all variable names are composed of strings and do not need to be declared. To assign a value to a variable, the format is as follows:

Variable name = Value

Note:

No space before and after equal sign (=)

For example:

X = 6

A = "how are you"

Assign the value of 6 to variable X, and assign the value of string "how are you" to variable.

4.2 Access variable value

To access the variable value, you can add a dollar sign "$" before the variable, for example:

[[Email protected] bin] # A = "how are you"

[[Email protected] bin] # echo "He juest said: $"

A is: Hello World

Values assigned to another variable can be written as follows:

Variable 2 =$ Variable 1

For example:

X = $ I

I ++ can be written as follows:

I = $ I + 1

4.3 enter the variable value on the keyboard

In shell programming, the variable value can be read from the keyboard as a string in the format:

Read variable

For example:

[[Email protected] bin] # Read Str

Read is a READ command that reads strings from the keyboard to Str.

Example 4: compile a shell program test3. When the program is executed, read a directory name from the keyboard, and then display the information of all files in the directory.

Analysis:

The variable that stores the directory is directory, and its read statement is:

Read directory

Command: ls-

[[Email protected] bin] # vi test3

#! /Bin/sh

Echo "Please input name of directory"

Read directory

CD $ directory

Ls-l

(2) Set permissions

[[Email protected] bin] # chmod + x test3

(3) Execution

[[Email protected] bin] #./test3

Note:

Enter the path "/"

Instance 5: run the program test4, read the values of X and Y from the keyboard, perform addition operations, and finally output the results.

(1) Use VI to edit the program

[[Email protected] bin] # vi test4

#! /Bin/sh

Echo "Please input x Y"

Read X Y

Z = 'expr $ x + $ y'

Echo "the sum is $ Z"

(2) Set permissions

[[Email protected] bin] # chmod + x test4

(3) Execution

[[Email protected] bin] #./test4

45 78

The sum is 123

Note:

Expression Total = 'expr $ total + $ num' and num = 'expr $ num + 1'. the symbol "'" is the "'" key in the upper left corner of the keyboard.