#!/usr/bin/env perl

# PURPOSE: distribute lines on input file(s) (or stdin) across multiple
# output files, determined by evaling some expression ARG1 in the context of
# the line having been read.

# EXAMPLE:

# put lines beginning with asdf or qwer in files name asdf.lines and qwer.lines respecively (ignoring other lines):
# distlines  '"$1.lines" if  m/^(asdf|qwer)/' 
# which COULD be written as a perl one-liner as
# perl -n -e 'next unless m/^(asdf|qwer)/; $path = "$1.lines"; open($o{$path}, "> $path") unless exists $o{$path}; select($o{$path}); print'

# put gff into one files per 
# distlines '@F=split; @F[3] if $#F=9'
use strict;
use warnings;
my $pathform = shift;
my %o;				# hash from paths to open filehandles
my $path = '';
my $lastpath;
while (<>) {
  $path = (eval $pathform) || $path;
  #die $path;
  if ($path) {
    if (! $lastpath ||  $path ne $lastpath) {
      $lastpath = $path;
      if (! exists $o{$path}) {
	  print STDERR $path . "\n";
	  open($o{$path}, "> $path") || die "opening $path" ;
      }
      select($o{$path}) || die "selecting $path";
    }
  }
  print $_ ;
}