Examine tracking code to get carrier

[TrapBarn]

I'm a Newbie of (seriously) advanced years and would appreciate a bit of help.

I have a metabox with 2 fields. First field is called tracking_number and the tracking number is entered manually. The second field is called tracking_url which is also entered manually.

The current code is as follows:-

// Examine the tracking url and return a provider name.
function dcwd_get_tracking_provider_from_url( $url ) {
    if ( strpos( $url, 'parcel.force.com' ) !== false ) {
        return 'Parcel Force';
    }
    if ( strpos( $url, 'royal.mail.com' ) !== false ) {
        return 'Royal Mail';
    }
    if ( strpos( $url, 'ups.com' ) !== false ) {
        return 'UPS';
    }
        
    // Unknown provider.
    return null;
}

I want to have the second field populated automatically based on examining the format of the tracking number in the tracking_number field. 
The format for the carriers I use are :-

Royal Mail = 21 alpha-numeric starting with 320..........
Parcel Force = 2 alpha followed by 7 digits 
UPS = 18 alpha- numeric starting with 1Z

Can someone oblige with the necessary adjustments, please?
 

[ginerjm]

All I see is a function that gives you something based upon what is in the url argument.  What is your definition of a "metabox"?  Is this some displayable tag or an input tag?  ??

[ginerjm]

PS - I would use the case-insensitive version of this function:  stripos.   Never know when the url might be different.