Undefined Variable In PHP Passing input name in url - php

Question

I have html form with post method. I want to pass the value of an input field in the url to the action page. I get undefined variable at first, but when I re-submit the form, I don't get undefined variable, I get the value I want.
Here is the code.
<div class="col-md-6 p-2">
<?php
if(isset($_POST['search'])){
$keyword = $_POST['keyword'];
}
?>
<form method="post" action="search.php?keyword=<?php echo $keyword;?>">
<div class="input-group">
<input type="text" name="keyword" class="form-control" placeholder="Enter a keyword eg: chinese">
<div class="input-group-append">
<button type="submit" name="search" class="form-control btn btn-success"><i class="icofont-search"></i> Search Videos</button>
</div>
</div>
</form>
<p></p>
</div>

Answer 1

You should declare $keyword variable before the if statement.
Try this
<?php
$keyword = null;
if(isset($_POST['search'])){
$keyword = $_POST['keyword'];
}
?>
Or
<form method="post" action="search.php?keyword=<?php echo $keyword ?? "";?>">

Answer 2

Problem in your example is this line <form method="post" action="search.php?keyword=<?php echo $keyword;?>"> this will return empty value in url.
you need a page to submit form in form action, so your codes should look like this:
<div class="col-md-6 p-2">
<?php
if(isset($_POST['keyword']) && !empty($_POST['keyword'])){
echo "Please type something to search";
}
?>
<form method="post" action="search.php">
<div class="input-group">
<input type="text" name="keyword" class="form-control" placeholder="Enter a keyword eg: chinese">
<div class="input-group-append">
<button type="submit" name="search" class="form-control btn btn-success"><i class="icofont-search"></i> Search Videos</button>
</div>
</div>
</form>
<p></p>
</div>
form action will pass parameters in url
And in search result page search.php :
if(isset($_GET['keyword'])){
$keyword = $_GET['keyword']; //Use filter value before searching database.
echo $keyword;
}