reliable user browser detection with php

Using an existing method (ie get_browser) is probably better than writing something yourself, since it has (better) support and will be updated with newer versions. There might be also usable libraries out there for getting the browser id in a reliable way.

Decoding the $_SERVER['HTTP_USER_AGENT'] is difficult, since a lot of browsers have quite similar data and tend to (mis)use it for their own benefits. But if you really want to decode them, you could use the information on this page for all available agent ids. This page also shows that your example output indeed belongs to IE 7. More information about the fields in the agent id itself can be found on this page, but as I said already browsers tend to use it for their own benefits and it could be in a (slightly) other format.

if stripos($_SERVER['HTTP_USER_AGENT'],"mozilla")!==false)

That's not a useful test, almost every browser identifies itself as Mozilla.

is $_SERVER['HTTP_USER_AGENT'] a reliable way?

No.

Should I instead opt for the get_browser function?

No.

Browser-sniffing on the server side is a losing game. Apart from all the issues of trying to parse the UA string, the browsers that lie, the obscure browsers, and the possibility the header isn't there at all, if you return different page content for a different browser you must set the Vary header to include User-Agent, otherwise caching proxies may return the wrong version of the page to the wrong browser.

But if you add Vary: User-Agent IE's broken caching code gets confused and reloads the page every time. So you can't win.

If you must browser-sniff, the place to do it is on the client side, using JavaScript and, specifically in IE's case, conditional comments. It's lucky that it's IE that supports conditional comments, since that's the one browser you often need workarounds for. (See scunliffe's answer for the most common strategy.)

Most PHP packages that I've found seemed to be pretty good but I couldn't find a good one that gave me everything I needed so I built a Laravel helper to combine 3 of them.

Here are the packages:

jenssegers/agent

whichbrowser/parser

cbschuld/browser.php

And here's my function:

function browser($userAgent)
{
    $agent = new \Jenssegers\Agent\Agent();
    $agent->setUserAgent($userAgent);

    $result = new \WhichBrowser\Parser($userAgent);

    $browser = new \Browser($userAgent);

    return new class($agent, $result, $browser)
    {
        public function __construct($agent, $result, $browser)
        {
            $this->agent = $agent;
            $this->result = $result;
            $this->browser = $browser;
        }
        public function device()
        {
            return $this->agent->device() ?: $this->result->device->toString() ?: $this->browser->getPlatform();
        }
        public function browser()
        {
            return $this->agent->browser() ?: $this->result->browser->name ?: $this->browser->getBrowser();
        }
        public function platform()
        {
            return $this->agent->platform() ?: $this->result->os->name ?: $this->browser->getPlatform();
        }
        public function isMobile()
        {
            return $this->agent->isPhone() ?: $this->result->isType('mobile') ?: $this->browser->isMobile();
        }
        public function isTablet()
        {
            return $this->result->isType('tablet') ?: $this->browser->isTablet();
        }
        public function isDesktop()
        {
            return $this->agent->isDesktop() ?: $this->result->isType('desktop') ?: (! $this->browser->isMobile() && ! $this->browser->isTablet());
        }
        public function isRobot()
        {
            return $this->agent->isRobot() ?: $this->browser->isRobot();
        }
    };

Here's how to use it:

$browser = browser($userAgent);

$browser->device();
$browser->platform();
$browser->browser();
$browser->isMobile();
$browser->isTablet();
$browser->isDesktop();
$browser->isRobot();

Something I notice, the real browser name always comes after the last (parentheses) with the exception of IE, where there is no browser name after the last (parentheses). I wonder if only reading after the last ) could improve accuracy.

you may notice this in different user agents:

Google Chrome

Safari

Firefox

Edge

IE (the exception where no browser is defined after parentheses)

example:

$userBrowser = (!empty($_SERVER['HTTP_USER_AGENT'])?$_SERVER['HTTP_USER_AGENT']:getenv('HTTP_USER_AGENT'));
$userBrowser = explode(')', $userBrowser);
$userBrowser = $userBrowser[count($userBrowser)-1];

echo $userBrowser; //this has many inaccurate browsers stripped out

A full function:

function getUserBrowser(){
  $fullUserBrowser = (!empty($_SERVER['HTTP_USER_AGENT'])? 
  $_SERVER['HTTP_USER_AGENT']:getenv('HTTP_USER_AGENT'));
  $userBrowser = explode(')', $fullUserBrowser);
  $userBrowser = $userBrowser[count($userBrowser)-1];

  if((!$userBrowser || $userBrowser === '' || $userBrowser === ' ' || strpos($userBrowser, 'like Gecko') === 1) && strpos($fullUserBrowser, 'Windows') !== false){
    return 'Internet-Explorer';
  }else if((strpos($userBrowser, 'Edge/') !== false || strpos($userBrowser, 'Edg/') !== false) && strpos($fullUserBrowser, 'Windows') !== false){
    return 'Microsoft-Edge';
  }else if(strpos($userBrowser, 'Chrome/') === 1 || strpos($userBrowser, 'CriOS/') === 1){
    return 'Google-Chrome';
  }else if(strpos($userBrowser, 'Firefox/') !== false || strpos($userBrowser, 'FxiOS/') !== false){
    return 'Mozilla-Firefox';
  }else if(strpos($userBrowser, 'Safari/') !== false && strpos($fullUserBrowser, 'Mac') !== false){
    return 'Safari';
  }else if(strpos($userBrowser, 'OPR/') !== false && strpos($fullUserBrowser, 'Opera Mini') !== false){
    return 'Opera-Mini';
  }else if(strpos($userBrowser, 'OPR/') !== false){
    return 'Opera';
  }
  return false;
}

echo 'browser detect: '.getUserBrowser();

I also tested this on chrome, edge, and firefox developer, and it worked accurately. (although I have not tested older versions of these browsers yet)

I think relying on the userAgent is a bit weak as it can (and is) often faked.

If you want to serve up CSS just for IE, use a conditional comment.

<link type="text/css" rel="stylesheet" href="styles.css"/><!--for all-->
<!--[if IE]>
  <link type="text/css" rel="stylesheet" href="ie_styles.css"/>
<![endif]-->

or if you just want one for IE6:

<!--[if IE 6]>
  <link type="text/css" rel="stylesheet" href="ie6_styles.css"/>
<![endif]-->

Since its a comment its ignored by browsers... except IE that loads it if the if test matches the current browser.

@Ekramul Hoque was on the right track but there are several flaws to his answer.

First of all, I would begin with Edge as Internet Explorer does not contain the term Edge in any of its UAs.

if(strpos($_SERVER['HTTP_USER_AGENT'], 'Edge') !== FALSE) {
  echo '<link type="text/css" href="ms.css" />';

Then, continue to work backward as earlier versions of IE didn't use the Trident engine and therefore won't contain it in their UA.

} elseif (strpos($_SERVER['HTTP_USER_AGENT'], 'Trident') !== FALSE) {
  echo '<link type="text/css" href="ms.css" />';
} elseif (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== FALSE) {
  echo '<link type="text/css" href="ms.css" />';

We need to target iOS browsers next so that the subsequent queries don't interfere with this one. All iOS browsers use webkit with the exception of Opera Mini, which does its rendering from a remote server instead of the device. This means that we can target the OS in the UA with iOS and exclude UAs that contain Opera.

} elseif (strpos($_SERVER['HTTP_USER_AGENT'], 'iOS') && !strpos($_SERVER['HTTP_USER_AGENT'], 'Opera') !== FALSE {
  echo '<link type="text/css" href="webkit.css" />';

Next, move on to Firefox browsers. While using Firefox for the search term will work, it will only identify Firefox browsers--not Firefox based browsers. Firefox contains Gecko in its UA as Gecko is the engine that it uses, and we can therefore target that. By using Gecko, we can identify all browsers that run on the Gecko engine (ie SeaMonkey). However, many browsers use the term like Gecko for compatibility reasons, so we must be sure to match Gecko and not like Gecko.

} elseif (strpos($_SERVER['HTTP_USER_AGENT'], 'Gecko') && !strpos($_SERVER['HTTP_USER_AGENT'], 'like Gecko') !== FALSE) {
  echo '<link type="text/css" href="moz.css" />';

Moving on we'll identify Opera browsers. Opera used the Presto engine to the end of v12. Starting with v15, they began using the Blink engine like Chrome. v12 and earlier contained two unique words in the UA that v15+ doesn't have--Opera and Presto. You can target either of them as they were always present together. For v15, Opera began using OPR in the UA.

} elseif (strpos($_SERVER['HTTP_USER_AGENT'], 'Presto') !== FALSE) {
  echo '<link type="text/css" href="o.css" />';
} elseif (strpos($_SERVER['HTTP_USER_AGENT'], 'OPR') !== FALSE) {
  echo '<link type="text/css" href="normal.css" />';

Next up is Safari. Safari uses AppleWebKit as its rendering engine, but we can't just target that because Chrome also includes both AppleWebKit and Safari in its UA for compatibility reasons. Therefore, we need to search for AppleWebKit and not Chrome.

} elseif (strpos($_SERVER['HTTP_USER_AGENT'], 'AppleWebKit') && !strpos($_SERVER['HTTP_USER_AGENT'], 'Chrome') !== FALSE) {
  echo '<link type="text/css" href="webkit.css" />';

Finally, we get to Chrome. Chrome used AppleWebKit until v27. With the v28 release, they switched over to the Blink engine. We could target both engines but it would require a lot of code. Being that Chrome is almost to v70 now, we'll just search for Chrome as it's highly unlikely anyone is still running a webkit version of Chrome.

} elseif (strpos($_SERVER['HTTP_USER_AGENT'], 'Chrome') !== FALSE {
  echo '<link type="text/css" href="normal.css" />';

And last but not least, your fallback/else.

} else {
  echo '<link type="text/css" href="normal.css" />';
}

Now, I used css files referring to the vendor prefix to target here. Feel free to tweak this as needed to have it do what you need it to do. I hope this helped.