I would use unpack or regexen or substr to extract the data ... the key is to move the values into variables on a reliable basis.

#!/usr/bin/perl   
use strict;   
use warnings;

#Open data file and put it into variable
open FILE, "<data.txt";
my $string = do {local $/; <FILE> };

my ($idx, $max) = (0, length $string );

while ( $idx < $max - 4 ) {
  my $fragment= substr( $string, $idx, 4 );
  $idx+= length $fragment;
  my $recordtype = substr( $string, $idx, 1 );
  $idx++;
  if ($recordtype eq '$') {
      print " record type: $recordtype\n";  
      print " data: $fragment\n";  
    }
  else {
    print "Non-dollar fragment: '$fragment', '$recordtype'\n";
  }
}
print "Unused portion of data file: ", substr( $string, $idx );
[download]

You will deduce I had a line break in my data.

record type: $
 data: 1234
Non-dollar fragment: 'qwer', 't'
Non-dollar fragment: 'asdf', 'g'
Non-dollar fragment: 'zxcv', 'b'
 record type: $
 data: !@#$
 record type: $
 data: 
?:"
[download]

Notice that if i come within 4 characters of the end, there are characters which can't be used duetot he lack of a recordtype.