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);