function variable question

craigh

I pulled a logfile code from online somewhere (maybe here) by Mattias Nilsson. It contains this function:

function get_var($name,$default) {
if($var = getenv($name)) {
return $var;
} else {
return $default;
}
}

I don't understand the value of $var...

The variable only occurs in the function. It's value does not appear to be set anywhere and then right away, the function is testing if ($var = ... etc.

what's the deal - am I just missing something in my PHP education? Also, shouldn't that if statement have a == instead of a =?

Anon

$var will be true if the value of the environment variable is returned. Or false if there is an error.

daarius

you are right.. its buggy var, and it should also contain ==

daarius

oh i see.... but still there should be ==

craigh

I'm still confused. What will be the value of $var if the condition is met?

daarius

well ok... actually this function is buggy.. the $var deffinately needs some initialised value in order to do comparission.

if thats not the case.. then you dont need the if statement, and just do:
return getenv($name);

thats it.

yelvington

No, all of you guys are confused.

$var is very clearly set. Read again the line

if($var = getenv($name))

The order of evaluation is as follows.

First, getenv() is called with $name as an argument. If the named environment variable exists, it returns the value of that variable. If not, it returns NULL.

Then, the result of getenv() is assigned to $var.

Then, the result of the assignment -- which is the same as the assigned value -- is tested.

If getenv() returned a value, then the tested value is true (i.e., not false).

If getenv() did not return a value, but rather NULL, then the tested value is false.

The code is correct.

craigh

AH - AHA, mhmm... I see now.

Honorable master - I thank you for your wisdom. :-)

Am I correct in assuming that the existence of these are tested because they may not be available on all servers? Also, am I correct in assuming that I can use phpinfo() to find out what environmental variables are available on my server?

thanks!

craigh

also - steve - if you don't mind - in this code:

function get_var($name,$default) {
if($var = getenv($name)) {
return $var;
} else {
return $default;
}
}

if($remote_host = get_var( "REMOTE_HOST", false)) {
$remote_host = get_var( "REMOTE_ADDR", "-");
}

if I replace the = with == in the if($remote_host line, it seems give $remote_host a value, if I leave as is, it always returns nothing. FWIW, REMOTE_HOST seems to not be available on my server.

which is right?

Anon

a less confusing method would be something like:

unset($var); / just to make sure it doesn't have a value /

$var = getenv($name);
if($var) {
...

the getenv function gets a value from an environment variable named $name (that is set on the command line for instance). This value is then returned to the $var variable.

getenv will generate a false value if there is no evironmental variable called $name... thus $var will be false....

Anon

the = symbol should be read "gets the value of".

the == symbol should be read "is equal to"

therefore you want

if($remote_host = get_var("REMOTE_HOST", false) {
...

which would read:
"if the variable $remote_host gets the value of get_var("REMOTE_HOST", false) is true, then..."

if you replace it with a == it reads:
"if the variable $remote_host is equal to the value of get_var("REMOTE_HOST", false) is true, then..."

this second statement means that if the value of $remote_host is the same as whatever get_var returns... probably not what you want, judging by syntax...

-Andy

Anon

I think the first method is correct. If the variable has no value that means that getenv() has not found a value in the environment variable. This means that the problem could be starting elsewhere. But I am not absolutely sure about this. It's a bit tricky. getenv() returns the value of the given environment variable or false if there is an error. It's only really useful if an environment variable changes after the script has started.
If you wish to give the environment variable a value use putenv().

I hope this is useful.

Anon

Yes. phpinfo() will give you a list of all the available environment vars.