putenv

(PHP 4, PHP 5, PHP 7)

putenv — 设置环境变量的值

说明

bool putenv ( string $setting )

添加 setting 到服务器环境变量。 环境变量仅存活于当前请求期间。 在请求结束时环境会恢复到初始状态。

设置特定的环境变量也有可能是一个潜在的安全漏洞。 safe_mode_allowed_env_vars 包含了一个以逗号分隔的前缀列表。 在安全模式下，用户可以仅能修改用该指令设定的前缀名称的指令。 默认情况下，用户仅能够修改以 PHP_ 开头的环境变量（例如 PHP_FOO=BAR）。 注意：如果此指令是空的，PHP允许用户设定任意环境变量！

safe_mode_protected_env_vars 指令包含了逗号分隔的环境变量列表，使用户最终无法通过 putenv() 修改。 即使 safe_mode_allowed_env_vars 设置允许修改，这些变量也会被保护。

参数

setting

设置，例如 "FOO=BAR"

返回值

成功时返回 TRUE， 或者在失败时返回 FALSE。

范例

Example #1 设置一个环境变量

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

注释

Warning

The safe_mode_allowed_env_vars 和 safe_mode_protected_env_vars 指令仅仅在启用安全模式时有效。

参见

User Contributed Notes

broussardrobert at sbcglobal dot net 23-Aug-2017 08:25
Multiple invocations of putenv() work as expected: the real problem was that some of the putenv() invocations in my script contained typographical errors.

I typed, e.g., putenv( "IMAGE_DATABASE=" . $_SERVER{'IMAGE_DATABASE'} );
which of course is incorrect.  '{' and '}' should have been '[' and ']'.
Because my first call to putenv() did not have that typo, it worked correctly, but the remaining three calls I coded with the typo merely cleared the corresponding environment variables and thus did not make it into the external script I invoked via a system() call.  I suspect the fact my first invocation was typed correctly affected my efforts looking at the syntax in the following invocations.

The trivial extension to the example provided is to merely call putenv() multiple times, once for each variable.
broussardrobert at sbcglobal dot net 23-Aug-2017 02:27
Great examples for the trivial case that most can figure out directly from the manual, but where is the trivially more complex example describing how to set multiple variables?  I tried separating with spaces, commas, semicolons, multiple invocations of setenv, all to no avail.  Please try to include trivial extensions to the examples...
Anonymous Coder 28-Mar-2012 03:28
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.
php at keith tyler dot com 22-Jun-2010 02:52
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
...
JM 17-Feb-2007 03:41
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
?>
david dot boyce at messagingdirect dot comnospam 14-Sep-2000 07:23
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.