in reply to replace/substituion 4th field

Considering you have already split up $line, why replace in the original? I would simply join @fields like so: 

while (my $line = <$data>) {

  chomp $line;

  my @fields = split ",", $line, -1;
  my $sum = $fields[3];
     

  $fields[3] = 'volemd'  if ($fields[3] >  310 ) ;
  $fields[3] = 'volemd1' if ($fields[3] == 70  ) ;

 print join( ',', @fields ) . "\n" ;

}

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Update: Modified as per correction by jwkrahn below.

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Re^2: replace/substituion 4th field
by jwkrahn (Abbot) on Feb 20, 2013 at 17:04 UTC 
      chomp $line;
 
  my @fields = split "," , $line;

  ...

 print join( ',', @fields ) . "\n" ;

    [download]

    That won't work correctly on the data provided.    You need to change split "," , $line to split "," , $line, -1.

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[d/l]
[select]

      Absolutely - Updated above.

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