Variable functionality in the shell

Local Variables :

Set Varname=value: scope for the entire bash process

Local Variables :

Local Varname=value: Scope is the current code snippet

Environment Variables :

Export Varname=value

or Varname=value export VARNAME

Positional variables :

$ ...

Special Variables :

$? : The execution status return value of the previous command

program execution, there may be two types of return values: 1. Program execution results, 2 program status return code (0-255), where 0 is executed correctly, 1-255: Error execution, 1,2,127 system reserved.

Common system Commands:

1. Undo Variable: Unset VARNAME

2. View variables in the current shell: Set view all variables (with environment variables and custom variables)

3. To view the environment variables for the current shell: printenv env Export

Keyboard reads and arrays of variables and declarations:

READ:-p to be followed by a prompt

DECLARE-[AIXR] Variable

A: Define a variable with the following name variable as an array type

I: Define a variable with the following name variable as an integer type

X: Define a variable with the following name variable as an environment variable

R: Set the variable to the readonly variable

#!/bin/bash
###
# #算奇数和偶数的和
var=100
Even=0
Odd=0
Declare-i i=0
While [$I-le $VAR]
Do
If [$ ($I%2))-EQ 0];then
even=$ (($EVEN + $I))
Else
odd=$ (($ODD + $I))
Fi
i=$ (($I + 1))
Done
echo "The odd number is: $ODD"
echo "The even number is: $EVEN"

Because strings are easier to handle in the shell, calculations for numeric values are not very easy to write. Simply Remember

For numeric processing, direct use of var=$ (OP content)

${array variable for the value of the array}

The following is a simple script to write a graphic:

#!/bin/bash
#绘制特殊图形
I=0
J=0
num=11
While [$I-le $NUM];
Do
If [$I-lt $ ((NUM/2))];then
tmp=$ (($NUM/2))
For ((t=0;t<$[$TMP-$I];t=t+1))
Do
Echo-n ""
Done
For ((k=0;k< $I; k=k+1))
Do
Echo-n "*"
Done
Echo
Else
For ((t=0;t<$[$I-$TMP];t=t+1))
Do
Echo-n ""
Done
For ((k=0;k<$[2* $TMP-$I];k=k+1))
Do
Echo-n "*"
Done
Echo
Fi
Let "I+=1"
Done

Loop structure

1.while [Condition]

Do

Done

2.until [Condition]

Do

Done

3.for var in con1 Con2 Con3

Do

Done

4.for (initial value; limit value; execution step))

Do

Done

#!/bin/bash
function Test1 () {
echo "The first way of looping"
Local i=0
Local sum=0
While [$I-le 100];
Do
sum=$[$SUM + $I]
Let "i++"
Done
The value of echo "SUM is:" $SUM
}
function Test2 () {
echo "Second way to Loop"
Local i=0
Local sum=0
Until [$I-le 100];
Do
sum=$ (($SUM + $I))
i=$[$I +1]
Done
The value of echo "SUM is:" $SUM
}
function Test3 () {
echo "The Third Way of looping"
Local i=0
Local sum=0
For I in ' SEQ 1 100 '
Do
sum=$ (($SUM + $I))
Done
echo "SUM value is $sum"

}
function Test4 () {
echo "Fourth cycle mode"
Local i=0
Local sum=0
For ((i=0;i<=100;i++))
Do
sum=$[$SUM + $I]
Done
The value of echo "SUM is:" $SUM
}
Test1
Test2
Test3
Test4

Variable functionality in the shell