That example is tame.What I'm writing now is running into 700 lines and, yep, you guessed it, understanding what the heck I was thinking is now becoming the problem - hence the need to get some rhyme and reason into what I'm doing.

And re it working - course it works!! It's a funny data set in this format

20/08/2007,Erythrocyte sedimentation rate,,3 mm/h
20/08/2008,Total white blood count,,6.7 10*9/L
and sometimes
04/04/2007,Haemoglobin estimation 12.9 g/dL,,12.9 g/dL
And a myriad other units.
[download]

Ah, your programs are becoming complex enough that the realization that there are always 2 people who need to understand the code is starting to sink in. Those 2 people are: (a) you when you write it and (b) you when you have to extend it or fix at some time in the future! And if it is a useful program, one of these 2 things and probably both will happen!

Some simplifications to the code will be possible, based upon your first example, I recoded the first part with some straightforward techniques and with just borrowing pretty much your regex'es. Your actual record is more complex. However, I hope that the lesson about spacing and indenting is becoming more clear - it helps a LOT.

#!/usr/bin/perl -w
use strict;

my $patient_id;   #patient record for the CSV file
my $nhs;
my $dob;
my $sex;
my $postcode;

my $total_patients=0;
while (<DATA>)
{
   s/^\s*//;  #remove leading space
   s/\s*$//;  #remove trailing space
   
   $patient_id = $1 if m/^Patient ID .*?(\d+)$/;
   $nhs        = $1 if m/^NAD .*?(\d+)$/;
   $dob        = $1 if m/^Date Of Birth .*?([\/\d]+)$/;
   $sex        = $1 if m/^Sex .*?(\w+)$/;
   
   #record ends with postal code -> output to the CSV file
   
   if ( ($postcode )= m/^Postcode .*?(\w+)$/ )
   {
      print "$patient_id,$nhs,$postcode,$dob,$sex\n";  #CSV line
      
      $total_patients++; # this is here instead of with $patient_id
                         # because it is here that we have an 
                         # "official"  patient record
      
      # this starts variables "over again". A runtime warning will
      # happen if for some reason one of these winds up still
      # being undefined when the record is printed to the CSV file
      #
      # note: doing this for $postcode is not necessary, but I
      # treat this variable same as the others because this lessens
      # the chance of a mistake when modifying the program later.
           
      $patient_id = $nhs = $dob = $sex = $postcode = undef;           
+           
   }   
}   

print "Total Patients: $total_patients\n";

=prints
1234,5678,BH78,01/01/1965,yes
4321,999,XYZ98,10/10/2007,no
Total Patients: 2
=cut

__DATA__
Patient ID 1234
NAD 5678
Date Of Birth : 01/01/1965
Sex  : yes
Postcode  : BH78
Patient ID 4321
NAD 999
Date Of Birth : 10/10/2007
Sex  : no
Postcode  : XYZ98
[download]

Simply moving the { makes such a difference and xxx = $1 again clarifies thinggs so much from an if loop. Thanks again.

I'm not sure what you want in this second programming problem. Maybe you could explain it a bit more?

This is a very simple CSV file (no quote characters or embedded quotes within quotes), so just split on the comma's and then do another split on space to get the basic value and measurement units from the line. I used what is called a list slice to assign directly to variables without any numeric subscript stuff.

The "formula" for this sort of thing is: open files, read and separate the input data into one "record" (a "quanta" if you will that makes sense for processing), either save that for processing in a collection of those "records" or process the records as you go.

In your first example, I don't think there is a need to save anything past the "current record". For this one, I don't know.. explain more and show more...

#!/usr/bin/perl 
use strict;
use warnings;   # the same as #!/usr/bin/perl -w in first line

while (<DATA>)
{
   next if /^\s*$/;     # skip blank lines
                        #   sometimes a last blank line
                        #   causes problems!
   s/\s*$//;            # or chomp;  fine also            
   
   my ($date, $description, $measurement) = (split (/,/,$_))[0,1,3];
   my ($value, $units) = split (/\s+/,$measurement);
   print "date     = $date\n",
         "descript = $description\n",
         "value    = $value\n",
         "units    = $units\n\n";

   # instead of print, do something here ...
}

=prints
date     = 20/08/2007
descript = Erythrocyte sedimentation rate
value    = 3
units    = mm/h

date     = 20/08/2008
descript = Total white blood count
value    = 6.7
units    = 10*9/L

date     = 04/04/2007
descript = Haemoglobin estimation 12.9 g/dL
value    = 12.9
units    = g/dL
=cut

__DATA__
20/08/2007,Erythrocyte sedimentation rate,,3 mm/h
20/08/2008,Total white blood count,,6.7 10*9/L
04/04/2007,Haemoglobin estimation 12.9 g/dL,,12.9 g/dL
[download]

If a new problem is being discussed, please start a new node.

It isn't a problem. What I was trying to do was give examples of the underlying data structures that was giving me the initial headache (but I forgot to show what comes after the headers that you cleverly deduced) The data structure is in the format

Patient ID 1234
NAD 5678
Date Of Birth : 01/01/1965
Sex  : yes
Postcode  : BH78

(as you guessed)

Then goes on to the gubbins
20/08/2007,Erythrocyte sedimentation rate,,3 mm/h
20/08/2008,Total white blood count,,6.7 10*9/L
04/04/2007,Haemoglobin estimation 12.9 g/dL,,12.9 g/dL
[download]

From that I split the data to 3 files One is a csv of basic information (anonomysed, all done within an encrypted face and DPA registered) and a second file of identifier, valuename, value A third file gives a simple list of every test that the script has come accross( that's the keys bit of the code) So I need to save the identifier as I go along, and add it to the lines that start with a date. Sorry for not being clear in the first place. But the next step will be to restructre all of this anong the lines that you've taught me. Thanks once again.