putenv

(PHP 4, PHP 5, PHP 7, PHP 8)

putenv — Sets the value of an environment variable

Description

putenv(string $assignment): bool

Adds assignment to the server environment. The environment variable will only exist for the duration of the current request. At the end of the request the environment is restored to its original state.

Parameters

assignment: The setting, like "FOO=BAR"

Return Values

Returns true on success or false on failure.

Examples

Example #1 Setting an environment variable

<?php
putenv("UNIQID=$uniqid");
?>

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User Contributed Notes 6 notes

down

php at keith tyler dot com ¶

14 years ago

putenv/getenv, $_ENV, and phpinfo(INFO_ENVIRONMENT) are three completely distinct environment stores. doing putenv("x=y") does not affect $_ENV; but also doing $_ENV["x"]="y" likewise does not affect getenv("x"). And neither affect what is returned in phpinfo().

Assuming the USER environment variable is defined as "dave" before running the following:

<?php
print "env is: ".$_ENV["USER"]."\n";
print "(doing: putenv fred)\n";
putenv("USER=fred");
print "env is: ".$_ENV["USER"]."\n";
print "getenv is: ".getenv("USER")."\n";
print "(doing: set _env barney)\n";
$_ENV["USER"]="barney";
print "getenv is: ".getenv("USER")."\n";
print "env is: ".$_ENV["USER"]."\n";
phpinfo(INFO_ENVIRONMENT);
?>

prints:

env is: dave
(doing: putenv fred)
env is: dave
getenv is: fred
(doing: set _env barney)
getenv is: fred
env is: barney
phpinfo()

Environment

Variable => Value
...
USER => dave
...

down

JM ¶

17 years ago

The other problem with the code from av01 at bugfix dot cc is that
the behaviour is as per the comments here, not there:
<?php
putenv('MYVAR='); // set MYVAR to an empty value.  It is in the environment
putenv('MYVAR'); // unset MYVAR.  It is removed from the environment
?>

down

domger at freenet dot de ¶

1 year ago

Values of variables with dots in their names are not output when using getenv(), but are still present and can be explicitly queried.

(saw this behaviour using PHP 8.2.4)

<?php

// set
putenv('foo.bar=baz');

// dump all
var_dump(getenv());    # <== variable 'foo.bar' NOT included, its value is not dumped

// dump explicitely 'foo.bar'
var_dump(getenv('foo.bar'));    # works, value 'baz' is shown

down

t7to7 ¶

5 years ago

White spaces are allowed in environment variable names so :

<?php
putenv('U =33');
?>

Is not equivalent to 

<?php
putenv('U=33');
?>

down

david dot boyce at messagingdirect dot comnospam ¶

24 years ago

Environment variables are part of the underlying operating system's

way of doing things, and are used to pass information between a parent

process and its child, as well as to affect the way some internal

functions behave.  They should not be regarded as ordinary PHP

variables.



A primary purpose of setting environment variables in a PHP script is

so that they are available to processes invoked by that script using

e.g. the system() function, and it's unlikely that they would need to

be changed for other reasons.



For example, if a particular system command required a special value

of the environment variable LD_LIBRARY_PATH to execute successfully,

then the following code might be used on a *NIX system:



<?php

 $saved = getenv("LD_LIBRARY_PATH");        // save old value

 $newld = "/extra/library/dir:/another/path/to/lib";  // extra paths to add

 if ($saved) { $newld .= ":$saved"; }           // append old paths if any

 putenv("LD_LIBRARY_PATH=$newld");        // set new value

 system("mycommand -with args");        // do system command; 

                        // mycommand is loaded using

                        // libs in the new path list

 putenv("LD_LIBRARY_PATH=$saved");        // restore old value

?>



It will usually be appropriate to restore the old value after use;

LD_LIBRARY_PATH is a particularly good example of a variable which it

is important to restore immediately, as it is used by internal

functions.



If php.ini configuration allows, the values of environment variables

are made available as PHP global variables on entry to a script, but

these global variables are merely copies and do not track the actual

environment variables once the script is entered.  Changing

$REMOTE_ADDR (or even $HTTP_ENV_VARS["REMOTE_ADDR"]) should not be

expected to affect the actual environment variable; this is why

putenv() is needed.



Finally, do not rely on environment variables maintaining the same

value from one script invocation to the next, especially if you have

used putenv().  The result depends on many factors, such as CGI vs

apache module, and the exact way in which the environment is

manipulated before entering the script.

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Anonymous Coder ¶

12 years ago

It's the putenv() type of environment variables that get passed to a child process executed via exec().

If you need to delete an existing environment variable so the child process does not see it, use:

putenv('FOOBAR');

That is, leave out both the "=" and a value.

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putenv

Description

Parameters

Return Values

Examples

See Also

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User Contributed Notes 6 notes