How do I check whether an environment variable is set in PHP?

Question

In PHP, how do I test whether an environment variable is set? I would like behavior like this:

// Assuming MYVAR isn't defined yet.
isset(MYVAR); // returns false
putenv("MYVAR=foobar");
isset(MYVAR); // returns true

Solution 1

getenv() returns false if the environment variable is not set. The following code will work:

// Assuming MYVAR isn't defined yet.
getenv("MYVAR") !== false; // returns false
putenv("MYVAR=foobar");
getenv("MYVAR") !== false; // returns true

Be sure to use the strict comparison operator (!==) because getenv() normally returns a string that could be cast as a boolean.

Solution 2

you can check like this

if($ip = getenv('REMOTE_ADDR'))
echo $ip; 

getenv() Returns the value of the environment variable.

Comments

[wecsam]

isset($var) is always true in this case.

[wecsam]

Isn't REMOTE_ADDR always set? In my case, I'm writing a script that needs to act differently based on whether the server has an environment variable set.

[Rajeev Ranjan]

@wecsam REMOTE_ADDR was just an example you can pass different environment variable

[wecsam]

I figured out by myself that getenv() returns false if the environment variable is not set. I see that that is what your code tries to illustrate. However, there are several problems with your code. First of all, we try to avoid using the = assignment operator in if conditionals because we almost always meant ==. Second of all, the value of the environment variable could be an empty string that casts to false, so we need to use a strict comparison operator.

[Rajeev Ranjan]

@wecsam I think its not comparison ,assign getenv('REMOTE_ADDR') value to $ip and then checking for $ip .

[wecsam]

I know that it's not a comparison. What I'm saying is that we usually don't do assignments in if conditionals.

[mostafa khansa]

@wescam is right, you can't do assignment inside an if condition

[nickdnk]

Since getvar() returns false when not set, isset will return true always, since $var is set, but set to false.

[boumbh]

I don't know why, but my PHP (7.1.32) returns an empty string when MYVAR is not defined... I triedkey_exists('MYVAR', getenv()), but it didn't work either, so I ended up checking for !empty(getenv('MYVAR'))...

[Fabien Snauwaert]

For people using DotEnv: values of OFF will be a string and so evaluate to true with this approach.

[Al-Amin]

What happened if my env variable ENV_VARIABLE=false ?