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# This module provides the same functionality as, but it
# uses the object-oriented interface.  It is a bit more general, as the
# programmer can create multiple path objects.
package srcclass;
use strict;

sub create {
    my $path;

    # Initialize from the current path or a default.
    if(exists $ENV{"PATH"}) {
        $path = $ENV{"PATH"};
        $path =~ s|/:|:|g;
        $path =~ s|/$||;
    } else {
        $path = "/bin:/usr/bin:/usr/local/bin";

    # The bless operation binds the reference to this class.
    return bless \$path;

# Get the current path.
sub the_path {
    my $self = shift @_;

    return $$self;

# Find the file on the path, and return the full path, or empty string.
sub find_file {
    my($self, $fn) = @_;

    my $pcom;
    foreach $pcom (split(/:/, $$self)) {
        if(-x "$pcom/$fn") { return "$pcom/$fn"; }

    return "";

# Add to the end of the path.
sub add_dir {
    my($self, $dir) = @_;

    $dir =~ s|/$||;
    $$self = "$$self:$dir";

# Add the first to the path before the second.  If no match found, not added.
# Return success.
sub add_dir_before {
    my($self, $dir, $beforethis) = @_;

    $dir =~ s|/$||;

    my($before, $after) = split(/:$beforethis:/, ":$$self:", 2);
    if($before ne ":$$self:") {
        $$self = "$before:$dir:$beforethis:$after";
        $$self =~ s/^://;
        $$self =~ s/:$//;

        return 1;
    else {
        return 0;


An object in perl is a reference which has been blessed. The reference can be to anything. Here it is a reference to an ordinary string, but a hash more commonly used. A reference is blessed by the built-in bless function. Bless creates an association between a reference and a package. (The reference is usually blessed into the package which creates and returns it, but any reference can be blessed into any package.) The association is used to interpret calls of the form


where $r is the blessed reference. It looks for the function f inside whatever package $r has been blessed into. If $r has been blessed into package Fred, then $r->f() becomes Fred::f($r). If there are more arguments in the call, say $r->f($a, "dandy"), then the call is Fred::f($r, $a, "dandy").
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