my( $H, $path ) = @_;
    
    # Chdir without arguments goes to home dir.
    # Can't use defined in test since $path may contain
    # a real null string.
    if ( ! $path and $path ne '0' ) {
        return 1;
    } elsif (chdir($path)) {
        $H->[1] = 0;
        return 1;
    } else {
        return;
    }

    my( $H ) = @_;
    
    # Go home unless we're already there
    if ($H->[1] == 0) {
        if (chdir( $H->[0] )) {
            $H->[1] = 1;
        } else {
            confess "Can't go home to [ ", $H->[0], ' ]';
        }
    }
}

1;

__END__

    my( $h, $path, $prog ) = @_;

    # Need to split path if $prog not provided
    unless ($prog) {
        ($path, $prog) = $path =~ m|(.*?)([^/]+)$|;
    }
    
    if (-l "$path$prog") {
        # Follow link
        _follow( $h, $path ) or return;
        unless (-x readlink($prog)) {
          confess "Can't read link '$path$prog' : $!";
	}
	my $link = $prog;
	$path = cwd() or confess "Can't determine cwd";
        return "$path/$prog";
    } elsif (-f _ and -x _) {
        # Return full path
        _follow( $h, $path ) or return;
        $path = cwd() or confess "Can't determine cwd";
        return "$path/$prog";
    } else {
        # Not a link or an executable plain file
        return;
    }
}

# To avoid unnecessary chdir'ing

    my $pkg = shift;
    foreach (@_) {
        #print STDERR "importing: $_\n";
        $Program_Paths{ $_ } = 0;
    }
    my( $home, @PATH, @missing );
    
    $home = cwd() or die "Can't save cwd";
    my $H = [ $home, 1 ];
    
    @PATH = split /:/, $ENV{'PATH'};
    foreach (@PATH) {
        s|/?$|/|; # Append / to each path
    }
    
    # For each program, check there is an executable
    foreach my $program (keys %Program_Paths) {
        
        # Deal with paths
        if ($program =~ m|/|) {
            _go_home( $H );
            my $path = $program;
            # Deal with tildes
            $path =~ s{^~([^/]*)}{ $1 ? (getpwnam($1))[7]
                                      : (getpwuid($>))[7] }e;
            if (my $real = _is_prog( $H, $path )) {
                $Program_Paths{ $program } = $real;
            }            
        }
        # Or search through all paths
        else {
            foreach my $path (@PATH) {
                _go_home( $H );
                if (my $real = _is_prog( $H, $path, $program )) {
                    $Program_Paths{ $program } = $real;
                    last;
                }
            }
        }
    }
    _go_home( $H ); # Return to home directory
    
    # Make a list of all missing programs
    foreach my $program (keys %Program_Paths) {
        push( @missing, $program ) unless $Program_Paths{ $program };
    }
    
    # Give informative death message if programs weren't found
    if (@missing) { 
        throw("Unable to locate the following programs as '". (getpwuid($<))[0]. "' on host '". hostname(). "' :\t".
        join ( " --> " , @missing )) ; 
    }
}

# Recursive function which follows links, or tests final destination

  Copyright (c) 1999-2009 The European Bioinformatics Institute and
  Genome Research Limited.  All rights reserved.

  This software is distributed under a modified Apache license.
  For license details, please see

    /info/about/code_licence.html

  Please email comments or questions to the public Ensembl
  developers list at <ensembl-dev@ebi.ac.uk>.

  Questions may also be sent to the Ensembl help desk at
  <helpdesk@ensembl.org>.

    use Bio::EnsEMBL::Analysis::Programs qw( efetch getz est2genome 
                     /usr/local/bin/this_one
                     ~me/some/path/my_prog
                     ~/../jane/bin/her_prog );

    # Can also do at run time
    Bio::EnsEMBL::Analysis::Programs->import( $someProg );

    $path_to_prog = $Bio::EnsEMBL::Analysis::Programs::Program_Paths{ $prog };