White spaces are allowed in environment variable names so :
<?php
putenv('U =33');
?>
Is not equivalent to
<?php
putenv('U=33');
?>
(PHP 4, PHP 5, PHP 7, PHP 8)
putenv — 设置环境变量的值
$setting
) : bool
添加 setting 到服务器环境变量。
环境变量仅存活于当前请求期间。
在请求结束时环境会恢复到初始状态。
setting
设置，例如 "FOO=BAR"
成功时返回 true， 或者在失败时返回 false。
Example #1 设置一个环境变量
<?php
putenv("UNIQID=$uniqid");
?>
White spaces are allowed in environment variable names so :
<?php
putenv('U =33');
?>
Is not equivalent to
<?php
putenv('U=33');
?>
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.
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...
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.
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
...
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
?>
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.