For perl code, you can visit http://www.bioperl.org/wiki/Main_Page. If you just want to extract the headers, on a Linux/Unix system, a simple grep "^>" myfile.fasta should work.

Why so complicated? ;) Only the header in a fasta file contains > so you can use grep :

grep -e ">" my.fasta

or awk to remove the >:

$ awk 'sub(/^>/, "")' 
>aksdjfljfd
aksdjfljfd

Expression in perl would be basically the same as the grep above (m/^>/).. There are easier 1-liner ways to do this, but this is a basic outline of the perl code that should be pretty readable.

#!/usr/bin/perl

open(FASTA, "<your.fa");
while(<FASTA>) {
    chomp($_);
    if ($_ =~  m/^>/ ) {
        my $header = $_;
        print "$header\n";
    }
}