php Validate latitude/longitude strings in decimal format

It's a bit old question, but anyway I post my solution here:

preg_match('/^[-]?(([0-8]?[0-9])\.(\d+))|(90(\.0+)?);[-]?((((1[0-7][0-9])|([0-9]?[0-9]))\.(\d+))|180(\.0+)?)$/', $geoResults['latlng']);

I assumed here that u split lat. from lng. by semicolon. If u want to check only lat. or only lng. here are regexp's;

Rgx for lat.:

/^[-]?(([0-8]?[0-9])\.(\d+))|(90(\.0+)?)$/

Rgx for lng.:

/^[-]?((((1[0-7][0-9])|([0-9]?[0-9]))\.(\d+))|180(\.0+)?)$/

Here is an improved online demo: https://regex101.com/r/bV5fA1/1

Add forward slashes to the beginning and end of the match sequence to make it valid regex syntax:

preg_match('/^(\-?\d+(\.\d+)?),\s*(\-?\d+(\.\d+)?)$/', $geoResults['latitude']);

For your question on whether to use regular expressions (regex) or not, in this case using regex (PCRE preg_match()) is the best way to secure your site. When matching variable complex string arrangements, regex is the way to go. It's common for developers to turn to regex for matching a static string such as 'abc'. This is when strpos() or str_replace() are better choices.