Getting Fasta sequences from a GFF

Some have whimpered, "How do I get a fasta file of the features in this GFF?"... Well, assuming your GFF file fits into memory (and assuming you have the appropriate fasta file to hand), here's how:

A script I like to call 'gff2fasta'

#!/usr/bin/perl -w
 
use strict;
use Bio::SeqIO;
 
my $verbose = 0;
 
 
 
## read in gff
 
warn "reading GFF\n";
 
my %gff;
 
open GFF, '<', 'my.gff3'
  or die "fail\n";
 
while(<GFF>){
  my ($seqid, undef, undef, $start, $end,
      undef, undef, undef, $attrs) = split;
 
  push @{$gff{$seqid}}, [$start, $end, $attrs];
}
 
warn "OK\n";
 
 
 
## Do the fasta
 
my $seqio = Bio::SeqIO->
  new( -file => 'my.fa',
       -format => 'fasta' )
  or die "double fail\n";
 
 
while(my $sobj = $seqio->next_seq){
  my $seqid = $sobj->id;
 
  unless(defined($gff{$seqid})){
    warn "no features for $seqid\n";
    next;
  }
 
  my $seq = $sobj->seq;
 
  for(@{$gff{$seqid}}){
    my ($start, $end, $attrs) = @$_;
 
    warn join("\t", $start, $end, $attrs), "\n"
      if $verbose > 0;
 
    my %attrs = split(/=|;/, $attrs);
 
    print ">$seqid-". $attrs{"ID"}.
      "/$start-$end (". ($end-$start+1). ")\n";
 
    print substr($seq, $start, $end-$start+1), "\n";
  }
 
  #exit;
}
 
warn "OK\n";