Question

An example would be

$ twice 15<br>
30<br>
$twice 0<br>
0<Br>
$

I understand that the basic of expr is

expr arg1 * arg2

What if I want to specify arg1 as 2 and arg2 as whatever the user types.

But I cant seem to make the program run, always a syntax error.
I use vi editor to make a new file and put the expr code in the file called (twice).

Answer 1

In the shell you need to escape the *-operator:

expr 2 \* 15

otherwise bash will replace it.

And in a script called twice.sh

#!/bin/bash
echo `expr 2 \* $1`

can then be called like this (after chmod 755 twise.sh)

./twice.sh 15

to print out 30.