Allow sorting to be combined and/or reversed

[ikiwiki.git] / doc / plugins / write.mdwn

diff --git a/doc/plugins/write.mdwn b/doc/plugins/write.mdwn
index bfa6617bd554d7f35b2f2f6b253abcf605db1245..1010e76e400bab3e479c081873437d37db0095f1 100644 (file)
--- a/doc/plugins/write.mdwn
+++ b/doc/plugins/write.mdwn
@@ -593,7 +593,9 @@ function of the ikiwiki wrapper when it is being generated.
        hook(type => "sort", id => "foo", call => \&sort_by_foo);
 
 This hook adds an additional [[ikiwiki/pagespec/sorting]] order or overrides
-an existing one. The callback is given two page names as arguments, and
+an existing one.
+
+The callback is given two page names followed by the parameter as arguments, and
 returns negative, zero or positive if the first page should come before,
 close to (i.e. undefined order), or after the second page.
 
@@ -603,6 +605,19 @@ For instance, the built-in `title` sort order could be reimplemented as
                pagetitle(basename($_[0])) cmp pagetitle(basename($_[1]));
        }
 
+and to sort by an arbitrary `meta` value, you could use:
+
+       # usage: sort="meta(description)"
+       sub sort_by_meta {
+               my $param = $_[2];
+               error "sort=meta requires a parameter" unless defined $param;
+               my $left = $pagestate{$_[0]}{meta}{$param};
+               $left = "" unless defined $left;
+               my $right = $pagestate{$_[1]}{meta}{$param};
+               $right = "" unless defined $right;
+               return $left cmp $right;
+       }
+
 ## Exported variables
 
 Several variables are exported to your plugin when you `use IkiWiki;`