use strict   ;
use warnings ;


sub del {

    my ( $delroadName, $delroadNumber ) = @_ ;  # This line handles params for function, 
                                                #    moved to first part of function

    my $process_file = "data.txt";              # Variable name changed to reflect action - 
                                                #    This kind of thing can mess things up later. 

    my @data ;
    { 

	# Adding additional scope to prevent missuse or error use of filehandle.

	open( my $data_file_handle, '<', "$process_file" )   # Changed to 3 param open and replaced bareword file handle.
	    or die("Can't open file: $process_file");        # Changed || to 'or' in case someone removes brackets for 'open'
                                                             #   Also added file name to error message.         

	@data = <$data_file_handle> ;               # NOTE: 'my' removed to ensure scope. 
	close( $data_file_handle );
    }



    chomp( @data ); 

    open( my $out_file_handle,'>', $process_file ) 
	or die("Can't open file: $process_file"); # Modified as above.

    foreach my $line_from_file ( @data ) {                     # Changed from for to foreach removed dependence on $_ 
	my @field = split( /\:/, $line_from_file );           

	# next if( ( $field[0] eq $delroadName ) && ( $field[1] == $delroadNumber ) ); 
	# Added brackets and changed $field[0] in both to [0] and [1]
	next if( ( $field[0] eq $delroadName ) && ( $field[1] == $delroadNumber ) ); 
	print $out_file_handle $line_from_file, "\n";         # Modified to print to file handle - Else the file will be truncated
                                                #   Since you are open is with '>' and will remain blank. 
    }

    # close $output;
    close $process_file;  # You want to close the file handle, not the string.

}