What to do if php trim doesn't work

Solution for php trim not working: first trim accepts parameters in reverse order; then set the string for masking characters from the beginning and end of the string; finally use str_replace function with empty replacement string That’s it.

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Specific questions:

Why doesn't my php trim() function work?

I'm trying to use trim to remove the underline characters from the data returned to the $_post array. I tried using

 $post_Value= str_replace("_", " ", $key)

but the text doesn't seem to be returned as a string. There is a break between each entrance. Then I tried trimming like this:

 <?php
$connection = mysqli_connect(DB_SERVER, DB_USER, DB_PASS, DB_NAME);
 // Test if connection succeeded
 if (mysqli_connect_errno())
    {
    die("Database connection failed: " . mysqli_connect_error() . " (" .  mysqli_connect_errno() . ")");
}
 if (isset($_POST))
    {
    $str = "";
   foreach($_POST as $key => $value)
    {
    $str = $str . $key . ",";
    }
   $post_Value = trim("_", $str);
   }
   $query = "UPDATE player_match SET categoryOption=&#39;$$post_Value&#39; WHERE id=1";
 ?>

When I use the trim function, nothing happens, it doesn't remove the _ characters. My ultimate goal is to put the comma separated list into the database as a single string. Why doesn't my trim() function work in this case?

Update:
was found in the view page resource, so I had to do a combination of the following:

 $post_Value= str_replace("<br_/>", "", $str);
        $post_Value2= str_replace("_", " ", $post_Value);
        $post_Value3= rtrim($post_Value2,",submit,");
        echo $post_Value3;
        $query="UPDATE player_match SET categoryOption=&#39;$post_Value3&#39; WHERE   id=1";

Workaround:

First, trim() accepts parameters in reverse order: $str, then $character_mask. So you should use: $post_Value = trim($str, "_");

Secondly, trim() only sets the string for masking characters from the beginning and end of the string. If the string is surrounded by non-shielded characters, no masking characters are removed from the string.

Actually, you should use str_replace() with an empty replacement string (you tried using a single space as the replacement):

$post_Value= str_replace("_", "", $key)

If you also want to remove the
tag (In its typical variation), this can be done with a single str_replace() call, like this:

$post_Value= str_replace(array("_", "<br>", "<br/>", "<br />"), "", $key)

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