Convert string on specific logic

Question

I would like to transfer a specific link to another. The patterns looks like this:

http://domain.com/sub/code/name to http://a.domain.com/subs/code/name

I need a one letter prefix before domain, the sub will be plural subs and thats all, all the rest needs to be equal.

Of course the link can start with http://, www, http://www

Some mix of substr_replace, strpos and explode, I stucked more than 1 hour on this task, decided to ask it.

Answer 1

Try this:

<?php
function convertLink($str)
{
    //ensure a scheme exists
    if(strpos($str,'http://')===false&&strpos($str,'https://')===false)
    {
        $str='http://'.$str;
    }
    $parts=parse_url($str);
    $scheme=$parts['scheme'];
    $domain=$parts['host'];
    $path=array_key_exists('path',$parts)?$parts['path']:'';
    $query=array_key_exists('query',$parts)?('?'.$parts['query']):'';
    $fragment=array_key_exists('fragment',$parts)?('#'.$parts['fragment']):'';

    if(strpos($parts['host'],'www.')===0){$domain=substr($parts['host'],4);}
    if(array_key_exists('port',$parts)){$domain.=':'.$parts['port'];}
    if(strpos($path,'/sub/')===0){$path='/subs/'.substr($path,5);}
    return "{$scheme}://a.{$domain}{$path}{$query}{$fragment}";
}

$links=array();
$links[]='domain.com/sub/code/name';
$links[]='domain.com:20/sub/code/name';
$links[]='www.domain.com/sub/code/name';
$links[]='http://domain.com/sub/code/name';
$links[]='http://www.domain.com/sub/code/name';
$links[]='https://domain.com/sub/code/name';
$links[]='sub.domain.com/sub/code/name';
$links[]='domain.com/sub/code/name?a=1&b=2#c';

echo '<pre>';
foreach($links as $link)
{
    echo str_pad($link, 40,' ',STR_PAD_RIGHT).'=> '.convertLink($link)."\n";
}
echo '</pre>';

Output:

domain.com/sub/code/name                => http://a.domain.com/subs/code/name
domain.com:20/sub/code/name             => http://a.domain.com:20/subs/code/name
www.domain.com/sub/code/name            => http://a.domain.com/subs/code/name
http://domain.com/sub/code/name         => http://a.domain.com/subs/code/name
http://www.domain.com/sub/code/name     => http://a.domain.com/subs/code/name
https://domain.com/sub/code/name        => https://a.domain.com/subs/code/name
sub.domain.com/sub/code/name            => http://a.sub.domain.com/subs/code/name
domain.com/sub/code/name?a=1&b=2#c      => http://a.domain.com/subs/code/name?a=1&b=2#c

Answer 2

Try something like this:

/^((?:http://)|(?:http://www\.)|(?:www\.))(\w+)(\.\w+\/)([\w+_\-]+)(\/.*?)$/

#$1YOUR_STRING.$2$3SOMETHING_ELSE$5

RegExr example: http://regexr.com?38dn0

Answer 3

What you are asking is fairly vague so I assume by "transfer" you mean "replace with". If that is the case, then you should look into Regular Expressions (or Regex).

Regular expressions are relatively universal, so when you learn them once, you can apply them with most languages.

In PHP, you can perform a Regex Replace with preg_replace, but it may help to read up a bit first on the different elements of patterns.

Relevant Links:

preg_replace PHP Function

PCRE Regex Syntax

EDIT: The end result you are after can still be achieved using strpos, explode etc as you described, but Regexs will likely get you there faster.