substr($body, 0, strpos($body, ' ', 260))

Your first approach is fine: Check whether x is contained with strpos and if so get anything after it with substr.

But you could also use strstr:

strstr($str, 'x')

But as this returns the substring beginning with x, use substr to get the part after x:

if (($tmp = strstr($str, 'x')) !== false) {
    $str = substr($tmp, 1);
}

But this is far more complicated. So use your strpos approach instead.

If your string has multibyte encoding (like UTF-8) does, you should use mb_substr to avoid problems like this:

$introtext=mb_substr($introtext,0,200);

The most efficient solution is the strtok function:

strtok($mystring, '/')

NOTE: In case of more than one character to split with the results may not meet your expectations e.g. strtok("somethingtosplit", "to") returns s because it is splitting by any single character from the second argument (in this case o is used).

@friek108 thanks for pointing that out in your comment.

For example:

$mystring = 'home/cat1/subcat2/';
$first = strtok($mystring, '/');
echo $first; // home

and

$mystring = 'home';
$first = strtok($mystring, '/');
echo $first; // home