Fast and simple solution:

$text = q(UFOFH 33603 01231 /0000 0024/ 1024/ 2025/ 3027/ 4030/ 5025/ 
+6028/ 7060/ 8081/ 9098/ 0110/ 1107/ 2106/ 3102/ 4080/ 5065/ 6057/) ;

$text =~ s/^UFOFH // and print split /\s+/,$text ;
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If the line you have in $text begins with "UFOFH ", it wipes it away and splits on spaces.

Cheers!
--bronto

Update: pure regexp solution:

$text = q(UFOFH 33603 01231 /0000 0024/ 1024/ 2025/ 3027/ 4030/ 5025/ 
+6028/ 7060/ 8081/ 9098/ 0110/ 1107/ 2106/ 3102/ 4080/ 5065/ 6057/) ;

$text =~ m|^UFOFH | and print "GOOOOHH!\n"
  if $text =~ m|([\d/]{5}\s?){4,27}|ig ;
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Update II:typo: you don't need the i when you are not matching alphabetics

Using the conditional if beginning of string matches... then match... should improve greatly the speed of the matching, compared to your solution. In fact, you are matching your pattern anywhere in the string, and that's expensive. The tecnique I used matches a short string at a specified position (the beginning of the line), and that's really fast! And if it doesn't match you don't waste your time trying to match your pattern against a string you are not interested in.

Anybody guessed I am in a hurry? :-)

# Another Perl edition of a song:
# The End, by The Beatles
END {
  $you->take($love) eq $you->made($love) ;
}

This should work according to your example:

#!/usr/bin/perl

use warnings;
use strict;

my $string = "UFOFH 33603 01231 /0000 0024/ 1024/ 2025/ 3027/ 4030/ 50
+25/ 6028/ 7060/ 8081/ 9098/ 0110/ 1107/ 2106/ 3102/ 4080/ 5065/ 6057/
+";

if ( $string =~ m#UFOFH ([\d/]{5}\s?){4,27}# ) {
    print "$string\n";
}
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Update: I updated the regexp to be a little prettier. Need more coffee...

I don't know how you wish to use the data but to split out each charac
+ter group 
(Except "UFOFH")into an array try this snippet

$_='UFOFH 33603 01231 /0000 0024/ 1024/ 2025/ 3027/ 4030/ 5025/ 6028/ 
+7060/ 8081/ 9098/ 0110/ 1107/ 2106/ 3102/ 4080/ 5065/ 6057/ <\p>';

my @mailbox=( m#([0-9//]{5})#g);

for my $i (0 .. $#mailbox) {
  print "mailbox[$i] =>  $mailbox[$i]\n";
};

which results in

mailbox[0] =>  33603
mailbox[1] =>  01231
mailbox[2] =>  /0000
mailbox[3] =>  0024/
mailbox[4] =>  1024/
mailbox[5] =>  2025/
mailbox[6] =>  3027/
mailbox[7] =>  4030/
mailbox[8] =>  5025/
mailbox[9] =>  6028/
mailbox[10] =>  7060/
mailbox[11] =>  8081/
mailbox[12] =>  9098/
mailbox[13] =>  0110/
mailbox[14] =>  1107/
mailbox[15] =>  2106/
mailbox[16] =>  3102/
mailbox[17] =>  4080/
mailbox[18] =>  5065/
mailbox[19] =>  6057/
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-_-_-_-_-_-_-_-_-_-_-_-
My memory concerns me
- but I forget why !!!
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But this only returns the penultimate charcter block before the newline

The last block is followed by a newline, not a blank, while in your regex there is a space trailing the block, so it does not match. Next problem, it only returns a single block because you match the entire string at once, but capture into always the same parens. So after one single iteration you have "eaten" the entire string, but you only get the last paren content.

$_ = q(UFOFH 33603 01231 /0000 0024/ 1024/ 2025/ 3027/ 4030/ 5025/ 602
+8/ 7060/ 8081/ 9098/ 0110/ 1107/ 2106/ 3102/ 4080/ 5065/ 6057/);

my @block;

if(/^UFOFH/gi) { # NB: /g is necessary for the following \G to work
    my @matches = m#\G\s([/\d]{5})#g;
    @block = splice @matches, 0, 27 if @matches >= 4;
}

print "@block\n";
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The \G is an anchor kind of like ^, except it does not match at the beginning of the string, but at the point where the previous /g match ended. As you see, it is slightly complicated to do this without split..

Update: I have a ways yet to go, obviously. The above solution bugged me, just slightly but it did. It took a day until I realized how to do it well - or more like, slap my forehead and say "D'oh".. This is the real thing (until further notice..):

my @matches = m#(?:^UFOFH|\G)\s([/\d]{5})#g;
my @block = splice @matches, 0, 27 if @matches >= 4;
print "@block\n";
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Thanks everyone for all your help. I have now got a working expression! And it is slightly neater than the previous effort...

The data structures are among email headers, which sometimes contain bits of the data. Unfortuantly not everyone sticks to quite the same data format, sometimes those /'s can be numbers, and the 'UFOFH' comes in a mixed case.

Thanks again

I "know" why you are not getting all the matches, and only the penultimate character block, but I can't seem to explain it right and don't want to misspeak. Hopefully someone else will properly explain that.

You regex can be improved as well
You can use \d instead of [0-9]
You have the / listed twice in your set.
There is no need for a set because your pattern is number followed by slash followed by space.
The reason you don't match out to the last item is because the last item does not have the trailing space. Perhaps you want to match space, number, slash instead.
Is it important that you get between 4 and 27 such blocks? What happens if the line has 29 of them? If it is not important then you don't need the {4,27} and can just use +.
Why are you using case-insensitive matching? Is the initial UFOFH possibly in mixed or lower case? If not, then the i is just slowing you down.

$mailbox =~ m#UFOFH( [\d/]{5}){4,27}# && print $&;
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$mailbox =~ m#^UFOFH( [\d/]{5}){4,27}$# && print $&;
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