Strictures are your friend (use strict; use warnings; - see The strictures, according to Seuss). In this case forcing you to declare variables with my may have made you think about the scope of $u_set and that may have led you to realize that the print is in the wrong place, and that may have led you to realize that the for loop was only performing one iteration, and that may have led you to notice that you used a tab character to split on instead of a comma. A better version of the code might look like:

use strict;
use warnings;
use Set::IntSpan;

my $TM_part1 = "25-40,74-93,95-120,130-149";
my $TM_part2 = "31-47,84-99,107-123,137-151";
my @split_TM1 = split(",", $TM_part1);
my @split_TM2 = split(",", $TM_part2);

for my $i (0 .. $#split_TM1) {
    my $set1 = Set::IntSpan->new($split_TM1[$i]);
    my $set2 = Set::IntSpan->new($split_TM2[$i]);
    my $u_set = intersect $set1 $set2;

    print "Union of strings: $u_set\n";
}
[download]

Note the Perlish for loop and avoidance of object indirect calling of the Set::IntSpan constructor.

It you want to do something pair-wise, just use pairwise :)

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11144630
use warnings;
use List::AllUtils qw( max min pairwise );

my $TM_part1="25-40,74-93,95-120,130-149";
my $TM_part2="31-47,84-99,107-123,137-151";

my @split_TM1 = split(",", $TM_part1);
my @split_TM2 = split(",", $TM_part2);

my $result = join ',', pairwise {
  my $low = max map /^(\d+)/, $a, $b;
  my $high = min map /-(\d+)/, $a, $b;
  $low <= $high ? "$low-$high" : ();
  } @split_TM1, @split_TM2;
print "$result\n";
[download]

Outputs:

31-40,84-93,107-120,137-149
[download]

It looks like your strings are comma-separated, but you are splitting them on tabs. You are also overwriting $u_set each time round the loop, so you'll need to accumulate the result differently.

I'd probably aim to write it something like this:

use strict;    # always
use warnings;  # always
use Set::IntSpan;

my $TM_part1 = "25-40,74-93,95-120,130-149";
my $TM_part2 = "31-47,84-99,107-123,137-151";

my @split_TM1 = split ',', $TM_part1;
my @split_TM2 = split ',', $TM_part2;

my $u_set = join ',', map {
  my $set1 = Set::IntSpan->new($split_TM1[$_]);
  my $set2 = Set::IntSpan->new($split_TM2[$_]);
  intersect $set1 $set2;
} 0 .. $#split_TM1;

print "Union of strings: $u_set\n";
[download]

.. but if you're not comfortable with map, you can accumulate the results in an array instead:

use strict;    # always
use warnings;  # always
use Set::IntSpan;

my $TM_part1 = "25-40,74-93,95-120,130-149";
my $TM_part2 = "31-47,84-99,107-123,137-151";

my @split_TM1 = split ',', $TM_part1;
my @split_TM2 = split ',', $TM_part2;

my @u_set;
for my $i (0 .. $#split_TM1) {
  my $set1 = Set::IntSpan->new($split_TM1[$i]);
  my $set2 = Set::IntSpan->new($split_TM2[$i]);
  push @u_set, intersect $set1 $set2;
}

my $u_set = join ',', @u_set;
print "Union of strings: $u_set\n";
[download]

Out of curiosity, and for a bit of fun, I wondered how a pure Perl solution would stack up against the two solutions using CPAN modules.

#!/usr/bin/env perl

use strict;
use warnings;

use Benchmark 'cmpthese';
use Test::More tests => 3;

my $TM_part1 = "25-40,74-93,95-120,130-149";
my $TM_part2 = "31-47,84-99,107-123,137-151";
my @split_TM1 = split ',', $TM_part1;
my @split_TM2 = split ',', $TM_part2;
my $union = '31-40,84-93,107-120,137-149';

is _span(), $union;
is _pair(), $union;
is _perl(), $union;

cmpthese 0 => {
    Span => \&_span,
    Pair => \&_pair,
    Perl => \&_perl,
};

sub _span {
    use Set::IntSpan;

    my @u_set;

    for my $i (0 .. $#split_TM1) {
        my $set1 = Set::IntSpan->new($split_TM1[$i]);
        my $set2 = Set::IntSpan->new($split_TM2[$i]);
        my $u_set = intersect $set1 $set2;

        push @u_set, $u_set;
    }

    return join ',', @u_set;
}

sub _pair {
    use List::AllUtils qw( max min pairwise );

    return join ',', pairwise {
        my $low = max map /^(\d+)/, $a, $b;
        my $high = min map /-(\d+)/, $a, $b;
        $low <= $high ? "$low-$high" : ();
    } @split_TM1, @split_TM2;
}

sub _perl {
    my @u_set;

    for my $i (0 .. $#split_TM1) {
        my %seen;

        for ([split /-/, $split_TM1[$i]], [split /-/, $split_TM2[$i]])
+ {
            ++$seen{$_} for $_->[0] .. $_->[1];
        }

        push @u_set, join '-', (sort grep $seen{$_} == 2, keys %seen)[
+0, -1];
    }

    return join ',', @u_set;
}
[download]

I ran that five times; here's a median result:

1..3
ok 1
ok 2
ok 3
         Rate Span Perl Pair
Span  16937/s   -- -20% -84%
Perl  21145/s  25%   -- -80%
Pair 106033/s 526% 401%   --
[download]

If you're interested, feel free to tweak the code for better (different) results.

I had to add SQL (postgres) :P

            Rate     Span SQL (Pg)     Perl     Pair
Span      8489/s       --     -44%     -56%     -86%
SQL (Pg) 15132/s      78%       --     -22%     -75%
Perl     19388/s     128%      28%       --     -68%
Pair     60727/s     615%     301%     213%       --
[download]

adding:

sub _sql {

  return $dbh->selectrow_arrayref("
select array_to_string( array(
  select lower(r) || '-' || upper(r)-1 from (
    select 
      (select unnest(r1) limit 1 offset n -1) *
      (select unnest(r2) limit 1 offset n -1)   as r
    from (values 
          (('{[' || replace(replace('$TM_part1', ',', '],['), '-', ','
+) || ']}')::int4multirange,
           ('{[' || replace(replace('$TM_part2', ',', '],['), '-', ','
+) || ']}')::int4multirange
          )) as f(r1,r2)
    , lateral generate_series(1, 4) as g(n)
  )       as g
), ',')   as h
;
")->[0] ;

}
[download]

Update: see my next message; it has improved/faster SQL and different Benchmark

I improved the SQL, this one here is a bit faster. I also include below changes to your test program, as lines to be added. The DBI connect will inevitably need some tweaking, depending on host machine.

use DBI;

#my $dbh = DBI->connect or die "hm - $@\n"; # easier when ENV vars are
+ set
my $dbh  = DBI->connect('dbi:Pg:', "app_user1", "P4ss_W0rd1") or die "
+meh - no db connection - $@\n" ;

# two test lines:

is _sql()     , $union;

"SQL/Pg"   => \&_sql,

# and the statement itself
sub _sql  { 

  return $dbh->selectrow_arrayref("

select array_to_string( array(
 select lower(isect) || '-' || upper(isect)-1 from(
  select
      ('['||replace(unnest(string_to_array('$TM_part1', ',')), '-', ',
+')||']')::int4range
    * ('['||replace(unnest(string_to_array('$TM_part2', ',')), '-', ',
+')||']')::int4range 
 ) as h(isect)
), ',')

")->[0] ;

}
[download]

and this is the new result:

              Rate     Span     Perl   SQL/Pg     Pair oneliner
Span        8373/s       --     -57%     -68%     -86%    -100%
Perl       19261/s     130%       --     -27%     -69%    -100%
SQL/Pg     26397/s     215%      37%       --     -57%    -100%
Pair       61443/s     634%     219%     133%       --     -99%
oneliner 5644800/s   67313%   29207%   21284%    9087%       --
[download]

perl -le "for($ARGV[0]=~/\-/g){my@a;map{$a[$_]++for(eval s/\-/\.\./r)}
+map{s/^([^,]*),?//;$1}@ARGV;print+(join'-',(grep$a[$_]==2,0..$#a)[0,-
+1])}"    
 
"25-40,74-93,95-120,130-149"     "31-47,84-99,107-123,137-151"

31-40
84-93
107-120
137-149
[download]

L*

PS this should be the sub to add to the above bench ( UPDATE it had many errors: corrected)

sub _oneliner{
        my @res;
        for($TM_part1=~/\-/g) { 
            my @arr;

            # map{ $arr[$_]++ for (eval s/\-/\.\./r) } map{ s/^([^,]*)
+,?//; $1 }$TM_part1, $TM_part2;
            # semplified a bit, see below

            map{s/^([^,]*),?//;$arr[$_]++ for( eval $1 =~ s/\-/\.\./r 
+)}$TM_part1,$TM_part2;
            push @res,(join'-',(grep { defined $arr[$_] and $arr[$_] =
+= 2 }0..$#arr)[0,-1] );
        }
        return join ',', @res;
}


__END__
1..4
ok 1
ok 2
ok 3
ok 4
               Rate     Span     Perl     Pair Oneliner
Span        12055/s       --     -27%     -84%    -100%
Perl        16553/s      37%       --     -79%    -100%
Pair        77602/s     544%     369%       --     -99%
Oneliner 11429533/s   94715%   68949%   14628%       --
[download]

UPDATE the double map is really redundant and unneeded in the above sub:

# map{$arr[$_]++ for(eval s/\-/\.\./r)}map{s/^([^,]*),?//;$1}$TM_part1
+,$TM_part2;
# should be:
    
map{s/^([^,]*),?//;$arr[$_]++ for( eval $1 =~ s/\-/\.\./r )}$TM_part1,
+$TM_part2;

# so also the oneliner can be reduced:

perl -le "for($ARGV[0]=~/\-/g){my@a;map{s/^([^,]*),?//;$a[$_]++for eva
+l$1=~s/\-/\.\./r}@ARGV;print join'-',(grep$a[$_]==2,0..$#a)[0,-1]}"
        "25-40,74-93,95-120,130-149"     "31-47,84-99,107-123,137-151"

31-40
84-93
107-120
137-149
[download]

PS I fixed 1..$#a with 0..$#a in the above code snippets