Difference between $ @ and $ * in Shell

$ @ Refers to all command line parameters. Each parameter is enclosed ""

$ * Indicates all command line parameters

 

The following procedure:

Test1.sh

-------------------

Sum = 0
For VaR
In "$ @"
Do
Let sum = sum + $ VaR
Done
Echo "sum = $ sum"

 

./Test1.sh 1 2 3

The result is sum = 6.

 

Test2.sh

--------------------

Sum = 0
For VaR
In "$ *"
Do
Let sum = sum + $ VaR
Done
Echo "sum = $ sum"

./Test2.sh 1 2 3

The result is sum = 1.

 

Analysis 1:

Bash-x test1.sh

The result is as follows:

+ Sum = 0
+ For VAR in '"$ @"'
+ Let sum = sum + 1
+ For VAR in '"$ @"'
+ Let sum = sum + 2
+ For VAR in '"$ @"'
+ Let sum = sum + 3
+ Echo sum = 6
Sum = 6

It can be seen that for is executed three times, indicating that for is bounded by "", because each parameter is surrounded ""

 

 

Analysis 2:

Bash-x test2.sh

The result is as follows:

+ Sum = 0
+ For VAR in '"$ *"'
+ Let sum = sum + 1 2 3
+ Echo sum = 1
Sum = 1

It can be seen that the loop is executed only once, indicating that $ * is surrounded by "" as a whole, not every parameter is surrounded by "", so it is only executed once

 

 

A more direct example is:

For VaR
In "a B C"
Do
Echo "$ {var }@"
Done

Print:

A B C @

 

For VaR
In "A" "B" "C"
Do
Echo "$ {var }@"
Done

Print:

A @

B @

C @