One, read receives keyboard input
read [options] [variable name]
Options:
-p prompt message
-t seconds
-n characters
-s hide input data
Example: Use the read prompt to enter the parameter value
result:
Compared with changes in position parameters, it is more friendly
Second, declare the variable type
+ Cancel type attribute of variable
-Set type attributes for variables
-a Set variable type to array
-i declare variable type as integer
-x declare variables as environment variables
-p displays the declared type of the variable
For example 1: a does not define a type, the default is a string, when a is defined as an integer (-i), when assigning a string to a, of course it will fail, the output is 0. View the properties of a (-p ), For plastic surgery
gjl@gjl-virtual-machine:~/shellTest$ declare -p a declare -- a="1" gjl@gjl-virtual-machine:~/shellTest$ declare -i a gjl@gjl-virtual-machine:~/shellTest$ a='we' gjl@gjl-virtual-machine:~/shellTest$ echo $a 0 gjl@gjl-virtual-machine:~/shellTest$ a=12 gjl@gjl-virtual-machine:~/shellTest$ echo $a 12 gjl@gjl-virtual-machine:~/shellTest$ declare -p a declare -i a="12"
Example 2: Declare b as an array and display the array
gjl@gjl-virtual-machine:~/shellTest$ declare -a c='([0]=1 [2]='11' [3]='aa')' gjl@gjl-virtual-machine:~/shellTest$ echo ${c[2]} 11
Array assignment
1. Add as needed
gjl@gjl-virtual-machine:~/shellTest$ b[0]=1 gjl@gjl-virtual-machine:~/shellTest$ b[1]=2 gjl@gjl-virtual-machine:~/shellTest$ echo ${b[*]} 1 2 gjl@gjl-virtual-machine:~/shellTest$ echo ${b[@]} 1 2
2. Add multiple elements at once
gjl@gjl-virtual-machine:~/shellTest$ declare -a c gjl@gjl-virtual-machine:~/shellTest$ c=(1 2 3) gjl@gjl-virtual-machine:~/shellTest$ echo ${c[*]} 1 2 3
3. Add in sparse format
gjl@gjl-virtual-machine:~/shellTest$ declare -a c='([0]=1 [2]='11' [3]='aa')' gjl@gjl-virtual-machine:~/shellTest$ echo ${c[2]} 11
The array is not in the order of 0123
4. Add by read -a
#!/bin/bash read -p "please input shuzu:" -a e echo ${e[*]} echo ${e[2]} gjl@gjl-virtual-machine:~/shellTest$ test07.sh please input shuzu:3 4 34 3 4 34 34
Note: When referencing variables, there must be at least curly brackets. Use brackets to represent the array. Array elements are separated by "space"
Delete a value in an array / delete an array
gjl@gjl-virtual-machine:~/shellTest$ echo ${c[*]} 1 2 3 gjl@gjl-virtual-machine:~/shellTest$ unset c[2] gjl@gjl-virtual-machine:~/shellTest$ echo ${c[*]} 1 2 gjl@gjl-virtual-machine:~/shellTest$ unset c gjl@gjl-virtual-machine:~/shellTest$ echo ${c[*]} gjl@gjl-virtual-machine:~/shellTest$
Cancel the type of variable
For example: a is an integer, use + to delete the integer attribute of a
gjl@gjl-virtual-machine:~/shellTest$ declare -p a declare -i a="12" gjl@gjl-virtual-machine:~/shellTest$ declare +i a gjl@gjl-virtual-machine:~/shellTest$ declare -p a declare -- a="12" gjl@gjl-virtual-machine:~/shellTest$
Three, operation
Three methods of numerical operations
①declare (not recommended)
②Use expr or let calculation tool (not recommended)
gjl@gjl-virtual-machine:~$ a=12 gjl@gjl-virtual-machine:~$ b=23 gjl@gjl-virtual-machine:~$ c=$(expr $a + $b) gjl@gjl-virtual-machine:~$ echo $c 35 gjl@gjl-virtual-machine:~$ let e=$a+$b gjl@gjl-virtual-machine:~$ echo $e 35 gjl@gjl-virtual-machine:~$ Matters needing attention: 1 , + space is required on both sides 2 , $ () means calling system command
③Use $ (()) or $ [] to perform numerical operations
gjl@gjl-virtual-machine:~$ a=11 ; b=33 gjl@gjl-virtual-machine:~$ echo c=$(($a+$b)) c=44 gjl@gjl-virtual-machine:~$ echo d=$[$a+$b] d=44 gjl@gjl-virtual-machine:~$
Example: Four arithmetic calculators (first edition)
#!/bin/bash read -t 30 -p "please input num1:" num1 read -t 30 -p "please input num2:" num2 read -t 30 -p "please input operato:[+-*/]:" oper [ "$oper" == "+" ] && echo "$(($num1+$num2))" && exit [ "$oper" == "-" ] && echo "$(($num1-$num2))" && exit [ "$oper" == "*" ] && echo "$(($num1*$num2))" && exit [ "$oper" == "/" ] && echo "$(($num1/$num2))" && exit echo "please input a varible operato"
Disadvantages and points of attention: num1 and num2 are not judged in this example. And [] needs spaces on both sides, otherwise it will report an error
4. Variable testing and content replacement
For example 1: If the variable a is not set, the x value is the new value. If a is set to null, the x value is null. If set to 123, the value of x is 123.
Can be used to test whether a variable exists or has a value
