How to validate user's input..?

Shell Programming and Scripting
1 
 $Input_filename=$ARGV[0];
	
if (!-d $Input_filename  && ! -e $Input_filename)
{
	print "USAGE: Please enter '$ABCD/def/dsed.txt' as an arguement \n";
	exit;
}
  1. Input Is suppose to be something like "$ABCD/def/dsed.txt".
    if the input is wrong the script should throw an ERROR message.

if user enters $ABCD only, error message should be displayed.

if the user enters "$ABCD/def/" a error message shold be displayed.

do i need any regex to check it out??

PLEASE SUGGEST.....

2

What programming/scripting language is this?

3

its perl...