You could use substr or unpack

use strict;
my $filename="0092042095432.dat"; #get this in as desired

#THEN with substr

my $fourchars=substr($filename,0,4);

# OR with unpack
my $fourchars=unpack("A4",$filename);

#THEN if you want each character you can
my @chars=split('',$fourchars);
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Now you have an array chars with the values (0, 0, 9, 2);

You want to read up on some basic documentation first, such as substr. To get the first four letters of your filename, you would do something like:

  my $filename = '0092042095432.dat';
  my $part     = substr( $filename, 0, 4 );
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Simple questions like this are best asked in the Chatterbox.

g r i n d e r

To take the case that the others have not answered so far, let's assume for a moment that the number of digits is always exactly the same each time and that you want to retrieve several bits of data from the filename. Try a regex. Long form:

use strict;

my ($this, $that, $tother, $twix);
my $fname = "0092042095432.dat";

if ($fname =~ /^(\d{4})(\d{3})(\d{3})(\d{3})/) {
   ($this, $that, $tother, $twix) = ($1,$2,$3,$4);
}
print "$this $that $tother $twix\n";   # ...or whatever
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($this, $that, $tother, $twix) 
      = $fname =~ /^(\d{4})(\d{3})(\d{3})(\d{3})/;
print "$this $that $tother $twix\n";   # ...or whatever
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