Contents of Directory Displayed using Arithmetic Expression

Mr. ameya sathe · 01-25-2008, 01:41 AM

Friday, January 25 2008, 12:58 IST

Dear Friends,
I executed the following command at bash command line.

Code:

echo Area: `expr $X \* $Y`
Output: Contents of the Present Working Directory similar to output of the command '
Code:
ls
' are displayed.

Question: How did this happen?

Yours,
Ameya

Guttorm · 01-25-2008, 02:52 AM

Hi

You forgot to set $X and $Y?

expr \*
Outputs:
*

So:
echo Area: *

Outputs:
"Area: " followed by the content of the current directory.

Remember bash evaluates the * before it executes the echo command.

It's a bit strange but it does make sense.

Mr. ameya sathe · 01-25-2008, 10:16 AM

Quote:

Originally Posted by Guttorm

Hi

You forgot to set $X and $Y?

Yes; I have deliberately not set the value of $X & $Y. Their values are undefined.

Quote:

Originally Posted by Guttorm

expr \*
Outputs:
*

So:
echo Area: *

Outputs:
"Area: " followed by the content of the current directory.
.

Thank you for explaining the derivation.

A new question has arisen in my mind; how come the execution of these commands
Code:
$echo *
$echo **
give the listing of the directory contents.

Yours,
Ameya

osor · 01-26-2008, 11:04 AM

I think you need to read up on how shell-globbing works.