my ($return_value) = the_function

not

my $return_value = the_function

You don't show the relevant code, but my guess is that the issue is scalar context vs. list context.

Most likely you have something like

sub nonblank {
    return grep { /\S/ } @_
}

print nonblank('foo'); # list context through print()
print $_ for nonblank('foo'); # explicit list context

my $temp= nonblank('foo'); # scalar context
print $temp; # still scalar

( $temp)= nonblank('foo'); # list context, discarding all but the firs
+t element
print $temp; # First element of that list

   $temp= (nonblank('foo'))[0]; # Scalar context in assignment, but we
+ only take the first element explicitly
print $temp;
[download]

... and grep returns a list, even if you are really, really certain that there will only ever be one matched element. And that list, when evaluated in scalar context turns into the number of elements. Which is 1.

I'm not using grep

my ($name) = seekName($id)
print "$name\n";

sub seekName
{
    my ($id) = $_[0];
    open (IN, "<:utf8", "names.txt") or die "Can't open: $!";
    
    seek In, $id, 0;
    my $line = <In>;
    return $line;
}
[download]

Output just gives a bunch of 1's

When I try to run the code you posted, I only get these errors:

C:\>perl -w tmp.pl
Name "main::IN" used only once: possible typo at tmp.pl line 8.
Use of uninitialized value $id in seek at tmp.pl line 10.
seek() on unopened filehandle In at tmp.pl line 10.
readline() on unopened filehandle In at tmp.pl line 11.
Use of uninitialized value $name in concatenation (.) or string at tmp
+.pl line 3.
[download]

Please try to make sure that the code you post actually exhibits the problem you are trying to diagnose.

When I change your code to the following:

my $id= shift;
my ($name) = seekName($id);
print "$name\n";

sub seekName
{
    my ($id) = $_[0];
    open (IN, "<:utf8", $0) or die "Can't open: $!";
    
    seek IN, $id, 0;
    my $line = <IN>;
    return $line;
}
[download]

... it assigns $name a value depending on what number I give on the command line. So I would assume that this works and does not exhibit the problem of always printing 1.

Context problem. Change the relevant line to:

my $name = seekName($id);

Alternate solution: return an array from your subroutine:

return ($line); Update: added the second alternate solution.

Could you please post your code so that we can help you better.

You need to check how you are printing the return value, scalar or list context.?