Technology Tales

Add Canonical Tags to WordPress without plugins

31^st March 2025

Search engines need to know which is which because they cannot know which is the real content when there is any duplication, unless you tell them. That is where canonical tags come in handy. By default, WordPress appears to add these for posts and pages, which makes sense. However, you can add them for other places too. While a plugin can do this for you, adding some code to your theme's functions.php file also does the job. This is how it could look:

function add_canonical_link() {
    global $post;

    // Check if we're on a single post/page
    if (is_singular()) {
        $canonical_url = get_permalink($post->ID);
    } 
    // For the homepage
    elseif (is_home() || is_front_page()) {
        $canonical_url = home_url('/');
    }
    // For category archives
    elseif (is_category()) {
        $canonical_url = get_category_link(get_query_var('cat'));
    }
    // For tag archives
    elseif (is_tag()) {
        $canonical_url = get_tag_link(get_query_var('tag_id'));
    }
    // For other archive pages
    elseif (is_archive()) {
        $canonical_url = get_permalink();
    }
    // Fallback for other pages
    else {
        $canonical_url = get_permalink();
    }

    // Output the canonical link
    echo '' . "\n";
}

// Hook the function to wp_head
add_action('wp_head', 'add_canonical_link');

// Remove default canonical link
remove_action('wp_head', 'rel_canonical');

The first part defines a function to define the canonical URL and create the tag to be added. With that completed, the penultimate piece of code hooks it into the wp_head part of the web page, while the last function gets rid of the default link to get avoid any duplication of output.

Fixing an update error in OpenMediaVault 4.0

10^th June 2019

For a time, I found that executing the command omv-update in OpenMediaVault 4.0 produced the following Python errors appeared, among other more benign messages:

Exception ignored in: <function WeakValueDictionary.__init__.<locals>.remove at 0xb7099d64>
Traceback (most recent call last):
File "/usr/lib/python3.5/weakref.py", line 117, in remove
TypeError: 'NoneType' object is not callable
Exception ignored in: <function WeakValueDictionary.__init__.<locals>.remove at 0xb7099d64>
Traceback (most recent call last):
File "/usr/lib/python3.5/weakref.py", line 117, in remove
TypeError: 'NoneType' object is not callable

Not wanting a failed update, I decided that I needed to investigate this and found that /usr/lib/python3.5/weakref.py required the following updates to lines 109 and 117, respectively:

def remove(wr, selfref=ref(self), _atomic_removal=_remove_dead_weakref):

_atomic_removal(d, wr.key)

To be more clear, the line beginning with "def" is how line 109 should appear, while the line beginning with _atomic_removal is how line 117 should appear. Once the required edits were made and the file closed, re-running omv-update revealed that the problem was fixed and that is how things remain at the time of writing.

Using NOT IN operator type functionality in SAS Macro

9^th November 2018

For as long as I have been programming with SAS, there has been the ability to test if a variable does or does not have one value from a list of values in data step IF clauses or WHERE clauses in both data step and most if not all procedures. It was only within the last decade that its Macro language got similar functionality, with one caveat that I recently uncovered: you cannot have a NOT IN construct. To get that, you need to go about things differently.

In the example below, you see the NOT operator being placed before the IN operator component that is enclosed in parentheses. If this is not done, SAS produces the error messages that caused me to look at SAS Usage Note 31322. Once I followed that approach, I was able to do what I wanted without resorting to older, more long-winded coding practices.

options minoperator;

%macro inop(x);
    %if not (&x in (a b c)) %then %do;
        %put Value is not included;
    %end;
    %else %do;
        %put Value is included;
    %end;
%mend inop;

%inop(a);

While running the above code should produce a similar result to another featured on here in another post, the logic is reversed. There are times when such an approach is needed. One is where a few possibilities are to be excluded from a larger number of possibilities. Since programming often involves more inventive thinking, this may be one of those.

%sysfunc and missing spaces

10^th June 2009

Recently, I was trying something like this and noted some odd behaviour:

data _null_;
    file fileref;
    put "text %sysfunc(pathname(work)) more text";
run;

This is the kind of thing that I was getting:

text c:\sasworkmore text

In other words, the space after %sysfunc was being ignored and, since I was creating and executing a Windows batch file using SAS 8.2, the command line action wasn't doing what was expected. Though the fix was simple, I reckoned that I'd share what I saw anyway, in case it helped anyone else:

data _null_;
    file fileref;
    x="text %sysfunc(pathname(work))"||" more text";
    put x;
run;