First of all, Yes, even you can use CPAN, and you can always copy the code from within modules into your program.

Second, are you sure that it works? Because after adding some print statements to your code to monitor its progress it seem to me that it's not doing anything sensible:

#!/usr/bin/perl
use strict;

#open DATA, "</home/file.conf";

my $DESIRED_LINE_NUMBER;
my $LINE;

while (<DATA>)
{
        if(m/END/)
        {
                print "END line is on line >$.\n";
                print "END line is >$_\n";
                my $pos = $.;
                $pos--;
                chomp $pos;
                $DESIRED_LINE_NUMBER = $pos;

        }
}

print "Moving to line number $DESIRED_LINE_NUMBER\n";

$. = 0;
do { $LINE = <DATA>; print "Discarding: $LINE\n" } until $. == $DESIRE
+D_LINE_NUMBER || eof;
print "Found desired line $DESIRED_LINE_NUMBER as '$LINE'\n";


__DATA__
foo
bar
baz
END
bloob
blargh
blubb
blubb2
[download]

But then again, if you're confident that it does what you want, most likely you're also able to modify it yourself to do more of what you want.

The modified program outputs:

C:\Projekte>perl -w tmp.pl
>4
>END

Moving to line number 3
Use of uninitialized value $LINE in concatenation (.) or string at tmp
+.pl line 2
6.
Discarding:
Use of uninitialized value $LINE in concatenation (.) or string at tmp
+.pl line 2
7.
Found desired line 3 as ''
[download]

... which doesn't look like the line above the END line to me.

This is an example... The match im trying to make is a commented filed in a file that has the pattern END in the string. So create a file with junk in it, put some commented field in the file #END. From here I need to be able to jump up one line, insert data, then place a new line under the new data. Some compaines restrict mod installs, as on platforms like aix, upgrades will sometimes render the mod usless, which is this case, so using CPAN is not an option. Even looking at TIE im not seeing an easy option for this.

open DATA, "</home/file.conf";

while (<DATA>)
{
        if(m/\END\b/)
        {
                print "$.\n";
                print "$_\n";
                $pos = $.;
                $pos--;
                chomp $pos;
                $DESIRED_LINE_NUMBER = $pos;

        }
}

#$. = 0;
do { $LINE = <DATA> } until $. == $DESIRED_LINE_NUMBER || eof;
print $LINE;
[download]

Result:

1675 ---> Line found matching Search
# *** END NEW MAPPING RULES SECTION *** ---Txt from Line

    -->Blank Line where I need to add values.
[download]