replace VARIABLE in $url string

I have a PHP code, which prints article from Wikipedia into my wordpress article. My problem is to replace VARIABLE in $url string

Let me explain my scenario.

VARIABLE is: post title of wordpress which have to be inserted in $url.

If single word in title, just insert it replacing VARIABLE in string in $url

if 2 words I need to replace the space (period) between words to %20

And the code, which solves it:

global $post;
$title = str_replace([" "], ["%20"], $post->post_title);
print $title;

This is the main php code I have. So what is the right way to get

<?php
$url =
    "http://en.wikipedia.org/w/api.php?action=query&prop=extracts|info&titles=**VARIABLE**&format=json&explaintext&redirects&inprop=url&indexpageids";

$json = file_get_contents($url);
$data = json_decode($json);
$pageid = $data->query->pageids[0];
$title = $data->query->pages->$pageid->title;
$string = $data->query->pages->$pageid->extract;

$getarticle = str_replace(
    ["==", "Biography", "References"],
    ["<br> <br>", "<b>Biography</b>", " "],
    $string
);

print $getarticle;
?>

$url = 'http://en.wikipedia.org/w/api.php?action=query&prop=extracts|info&titles=$title&format=json&explaintext&redirects&inprop=url&indexpageids';

• Parse the URL using parse_url function.
• Get the query params using query key from the output of the above function.
• Explode based on & and add your $title variable to titles key.
• Implode the query string back and make your URL again.

Snippet:

<?php

$parsed_url = parse_url($url =
    "http://en.wikipedia.org/w/api.php?action=query&prop=extracts|info&titles=**VARIABLE**&format=json&explaintext&redirects&inprop=url&indexpageids");

$params = [];

parse_str($parsed_url['query'], $params);

$title = 'Some example';// $data->query->pages->$pageid->title;

$params['titles'] = $title;

$parsed_url['query'] = http_build_query($params);

$url = $parsed_url['scheme'] . '://' . $parsed_url['host'] . $parsed_url['path']. '?' . $parsed_url['query'];

echo $url;

Online Demo