if( $line =~ /TITLE/)
{
  $line =~ s/TITLE#(.*)#/$1/;
  chomp($1);
}
else if ( $line =~ /DATA-A/)
{
  $line =~ s/DATA-A#(.*)#/$1/;
  chomp($1);
}
[download]

For your table formatting, take a look at Text::Table.

Here's a quick take at some code to extract the data from your files. Take a close look at your regexes, they don't need to be substitutions, and the use of the greedy '.*' will cause you to get wrong values on lines with multiple tags.

# Assume a FIELD#...# string can't be split across lines.
use strict;
use warnings;

use Data::Dumper;


my @DATA_FIELDS = (
    'TITLE',
    'DATA-A', 
    'DATA-B',
    'DATA-C',
);

# Build a regex that matches all fields and extracts a value.
my $all_fields = join '|', @DATA_FIELDS;
my $DATA_REGEX = qr/($all_fields)#([^#]*)#/;


my @data;               # store all tag data
my $title_data = {};    # reference to current title's data store.

while (<DATA>) {
    
    # the /g
    while ( /$DATA_REGEX/g  ) {
        my $field = $1;
        my $value = $2;

        print "$_ -> $field, $value\n";
    
        if( $field eq 'TITLE' ) {

            # store previous title data set if not empty.
            push @data, $title_data
                if %$title_data;

            # start new title data set
            $title_data = { TITLE => $value };
        } 
        else {
            # store field data in current title data set.
            push @{ $title_data->{$field} }, $value;
        }
    }
    
}

# store final title data set
push @data, $title_data
    if %$title_data;

print Dumper \@data;


__DATA__


asdf
asdfg=4eafvasdfadsf
ashfasdf
asdf qer qwer
asd as dsasdi weeiwer dfhjTITLE#How are you#asdfads
asdfa

asdg
rt
wqrqw
re

DATA-A#item1#asdfdasfdasdasDATA-B#item2#
asdfda
dasfa


asdfdas
DATA-C#item3#
aasdfDATA-A#item1a#DATA-B#item2b#

asd
asdf
asdDATA-C#item3c#
asdf asdf3132 adsf TITLE#I am fine#ads fadsfdasfdas
[download]


TGI says moo

I'm not sure what to say to answer your actual questions, but I suspect that

$line =~ s/DATA-A#(.*)#/$1/;
[download]

may not do what you actually want. It removes "DATA-A#" and the final "#" from the line. So, for instance, given the line

aasdfDATA-A#item1a#DATA-B#item2b#

from your sample data, it would produce

aasdfitem1a#DATA-B#item2b

Assuming you're trying to extract the text "item1a" from the line, the regex you want is

$line =~ /DATA-A#([^#]*)#/;
[download]

which extracts "item1a" into $1 (without destroying the rest of the line, so the DATA-B will still be there to collect later). Using [^#]* instead of .* will cause it to stop capturing at the first # it sees instead of continuing to the last one.

I suppose something like

my %data = ();
while ($line =~ /(TITLE|DATA-[ABC])#([^#]*)#/g) {
  $data{$1} = $2;
  handle_data($data{TITLE}, $data{DATA-A}, $data{DATA-B},
              $data{DATA-C}) if $1 eq 'DATA-C';
}
[download]

might be what you're looking for here, but I'm not entirely sure. Note the assumption that you identify the end of a data set by the appearance of a DATA-C element. handle_data would then either print the data, store it for later formatting, or whatever else may need to be done with it. Other initialization and/or sanity checking is probably needed unless your input stream is known to be perfect and will never, say, send an ITEM-C before all of the other elements have appeared.

update: Added a forgotten ) in the last code fragment. This code is (obviously) untested. If it breaks, you get to keep both pieces.

You should use 'elsif' and not 'else if'.