my $string = "TE=ASR,EV=R,PPF=G1,TG=G1,TMT=P1,RTV=YE,AAT=0,AT=105,ON=Y
+,CF1=FGOC";

my @fields    = split /,/, $string;
my $per_group = int(@fields / 4);
my $extras    = @fields - $per_group*4;

while (@fields) {
   my $n = $per_group;
   if ($extras) { $extras--; $n++; }
   print(join(',', splice(@fields, 0, $n)), "\n");
}
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