$re = '/"_id[^,]*,\s*/m';
$str = 'json_file<- \'{ "_id" : ObjectId( "539163d7bd350003" ), "login" : "vui", "id" : 369607, "avatar_url" : "https://avatars.mashupsusercontent.com/u/369607?", "gravatar_id" : "df8897ffebe16c5b0cd690925c63e190", "url" : "https://api.mashups.com/users/vui", "html_url" : "https://mashups.com/vui", "followers_url" : "https://api.mashups.com/users/vui/followers", "following_url" : "https://api.mashups.com/users/vui/following{/other_user}", "gists_url" : "https://api.mashups.com/users/vui/gists{/gist_id}", "starred_url" : "https://api.mashups.com/users/vui/starred{/owner}{/repo}", "subscriptions_url" : "https://api.mashups.com/users/vui/subscriptions", "organizations_url" : "https://api.mashups.com/users/vui/orgs", "repos_url" : "https://api.mashups.com/users/vui/repos", "events_url" : "https://api.mashups.com/users/vui/events{/privacy}", "received_events_url" : "https://api.mashups.com/users/vui/received_events", "type" : "User", "site_admin" : false, "org" : "amurath" }\'
';
$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