$re = '/"union[^}]+}\s*,/m';
$str = ' json<- \'{"open_issues":0,"union":{"avatar_url":"https://secure.gravatar.com/avatar/ed73cf7f24c091318e507d167c7b3456?d=https://a248.e.akamai.net/assets.mashups.com%2Fimages%2Fgravatars%2Fgravatar-orgs.png","gravatar_id":"ed73cf7f24c091318e507d167c7b3456","id":1556245,"login":"Toolpark","url":"https://api.mashups.com/users/Toolpark"},"owner":{"avatar_url":"https://secure.gravatar.com/avatar/ed73cf7f24c091318e507d167c7b3456?d=https://a248.e.akamai.net/assets.mashups.com%2Fimages%2Fgravatars%2Fgravatar-orgs.png","gravatar_id":"ed73cf7f24c091318e507d167c7b3456","id":1556245,"login":"Toolpark","url":"https://api.mashups.com/users/Toolpark"},"private":false,"pushed_at":"2012-07-12T11:43:31Z","size":964,"ssh_url":"vit@mashups.com:Toolpark/irma.vit","svn_url":"https://mashups.com/Toolpark/irma","updated_at":"2012-07-12T11:43:31Z","url":"https://api.mashups.com/repos/Toolpark/irma","watchers":2}\'
';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php