This might not be exactly what you're after, but I wrote it how I'd approach things. and I added more comments than I normally would in order to make it clear what direction I was after and explain things. It appears to do what you want.

#!/usr/bin/perl

use warnings;
use strict;

use FindBin qw($Bin);
use Tie::File;

# A list of IPs and subnet masks to substitute for '*' as we read thro
+ugh a file of share info. If
# you need this from a file, consider File::Slurp.
my @ips = qw(192.169.32.0/255.255.255.0
             192.169.72.0/255.255.255.0
             192.169.73.0/255.255.255.0);

# The path and name of the share file.
my $sharefile = "$Bin/sharefile";

# Will hold the position in the @ips array as we progress through the 
+file looking for matches.
my $last_index = '0';

# Holds the contents of the share file.
my @contents;

# This maps array elements to lines in the share file.
tie(@contents, 'Tie::File',  $sharefile) or die "Cannot tie $sharefile
+: $!\n";

# Read each line in the file. If we see a '*' we replace it with an en
+try in the @ips array. If a
# replacement happens, we increment $last_index to point to the index 
+number of the next element in
# the @ips array. If we matched the last element, we reset the counter
+ back to zero and start at
# the beginning.
for (my $i = 0; $i <= $#contents; $i++) {
  if ($contents[$i] =~ s/\*/$ips[$last_index]/) {
    if (++$last_index == @ips) {
      $last_index = '0';
    }
  }
}

untie(@contents);
print "Done editing $sharefile.\n";
[download]

That assumes you have the share info in a file called 'sharefile' in the same directory as the script. After running, the sharefile file looks like this:

/file1 192.169.32.0/255.255.255.0(rw,sync,no_root_squash,no_subtree_ch
+eck)
/file1 192.169.72.0/255.255.255.0(rw,sync,no_root_squash,no_subtree_ch
+eck)
/file1 192.169.73.0/255.255.255.0(rw,sync,no_root_squash,no_subtree_ch
+eck)

/file2 192.169.32.0/255.255.255.0(ro,sync,no_root_squash,no_subtree_ch
+eck)
/file2 192.169.72.0/255.255.255.0(ro,sync,no_root_squash,no_subtree_ch
+eck)
/file2 192.169.73.0/255.255.255.0(ro,sync,no_root_squash,no_subtree_ch
+eck)
# shares for Tsp InstallServer
file3 192.169.32.0/255.255.255.0/255.255.255.0(ro,sync,no_subtree_chec
+k)
file3 192.169.72.0/255.255.255.0/255.255.255.0(ro,sync,no_subtree_chec
+k)
file3 192.169.73.0/255.255.255.0/255.255.255.0(ro,sync,no_subtree_chec
+k)
[download]

I think that's what you were after anyway...