#To process every line of those files one at a time, use:

{
    local @ARGV = <*.txt>;
    while( <> ) {
        # $_ contains the lines of the files one at a time; for each file in turn
        # To display file(line no): line for every .txt file in the current directory use:
        chomp; print $ARGV, '(', $., '):', $_; 
    }
}