Getting the last revision number in SVN?

<?php
    $url = 'your repository here';
    $output = `svn info $url`;
    echo "<pre>$output</pre>";
?>

You can get the output in XML like so:

$output = `svn info $url --xml`;

If there is an error then the output will be directed to stderr. To capture stderr in your output use thusly:

$output = `svn info $url 2>&1`;

If you want to analyse a local working copy, the best tool is svnversion, which comes with Subversion and produces output like 968:1000M. The documentation says:

The version number will be a single number if the working copy is single revision, unmodified, not switched and with an URL that matches the TRAIL_URL argument. If the working copy is unusual the version number will be more complex:

4123:4168     mixed revision working copy
4168M         modified working copy
4123S         switched working copy
4123:4168MS   mixed revision, modified, switched working copy