PHPKonf: Istanbul PHP Conference 2017


(PHP 4, PHP 5, PHP 7)

putenvEstablece el valor de una variable de entorno


bool putenv ( string $setting )

Agrega setting al entorno del servidor. La variable de entorno existirá únicamente durante la petición actual. Al final de la petición el entorno es recuperado a su estado original.

Definir ciertas variables de entorno puede representar una brecha de seguridad potencial. La directiva safe_mode_allowed_env_vars contiene una lista de prefijos delimitados por comas. En Modo Seguro, el usuario puede alterar únicamente variables de entorno cuyos nombres comiencen con los prefijos ofrecidos por esta directiva. Por omisión, los usuarios sólo podrán definir variables de entorno que comiencen con PHP_ (p.ej. PHP_FOO=BAR). Nota: si esta directiva se encuentra vacía, ¡PHP permitirá que el usuario modifique CUALQUIER variable de entorno!

La directiva safe_mode_protected_env_vars contiene una lista de variables de entorno delimitadas por comas, que el usuario final no podrá modificar usando putenv(). Estas variables serán protegidas incluso si safe_mode_allowed_env_vars se establece de tal modo que permita modificarlas.



El parámetro, como p.ej. "FOO=BAR"

Valores devueltos

Devuelve TRUE en caso de éxito o FALSE en caso de error.


Ejemplo #1 Definición de una variable de entorno




La directiva safe_mode_allowed_env_vars y safe_mode_protected_env_vars sólo tendrán efecto cuando safe_mode esté habilitado.

Ver también

  • getenv() - Obtiene el valor de una variable de entorno
  • apache_setenv() - Establece una variable subprocess_env de Apache

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User Contributed Notes 4 notes

php at keith tyler dot com
6 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:

print "env is: ".$_ENV["USER"]."\n";
"(doing: putenv fred)\n";
"env is: ".$_ENV["USER"]."\n";
"getenv is: ".getenv("USER")."\n";
"(doing: set _env barney)\n";
"getenv is: ".getenv("USER")."\n";
"env is: ".$_ENV["USER"]."\n";


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


Variable => Value
USER => dave
9 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:
('MYVAR='); // set MYVAR to an empty value.  It is in the environment
putenv('MYVAR'); // unset MYVAR.  It is removed from the environment
Anonymous Coder
4 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:


That is, leave out both the "=" and a value.
david dot boyce at messagingdirect dot comnospam
16 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

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:

= 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

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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