What happens to argument in alias after using it once? [duplicate]

Question

Why does this only print arg out once?

$ alias test="echo $1 $1 $1"
$ test arg
arg

This is on GNU bash, version 4.2.25(1)-release (x86_64-pc-linux-gnu).

Answer 1

List aliases with alias command after you defined that alias and you will clearly understand it:

alias test="echo $1 $1 $1"
alias

Output:

alias test='echo   '

It simply expands to a string with variables only which were defined at execution time. So this for example works (Vvariable MY_VAR is defined):

MY_VAR="foo"
alias test="echo $MY_VAR $MY_VAR $MY_VAR"
alias

Output:

alias test='echo  foo foo foo'

You can replace it with function

function test() {
    echo $1 $1 $1
}

Answer 2

I doubt if alias supports $1,$2,... Its help keeps silence on that.

So I think that your command test arg is expanded like echo $1 $1 $1 arg. Where $1 is empty and you get your result.

1 more example:

$ alias test='echo $1 $1 $1'
$ test arg1 arg2
arg1 arg2

In the above example the alias test=... get's executed and the net effect is we're let with an alias to the command echo. We can see this effect when we run the command test arg1 arg2. All we're doing is running echo and passing it the strings arg1 and arg2.

$ echo arg1 arg2