$fh = <>; #first line of input is FT
chomp $fh; #get rid of newlines
$/ = "\nBH"; #set Input record seperator to newline followed by BH
while (<>) { #loop through each chunk
    @lines = split /\n/,$_; #split chunk into lines
    chomp @lines; #get rid of newlines;
    $bh = shift @lines; #BH is first line.
    $ft = pop @lines; #on last iteration FT will be last line, otherwise the lastline is a bare BH
    ($bh =~ /^BH/) || ($bh .= "BH" . $bh");  #if $bh doesn't start with BH then put it back.
    foreach $trans (@lines) {
        process($trans, $bh); #each remaining line is a single transaction line
    }
}