PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

450 Chapter 19 Interacting with the File System and the Server
way, you stop users from maliciously (or otherwise) executing commands on your system.You
can call it like this:
system(escapeshellcmd($command));
You should also use the escapeshellarg() function to escape any arguments you plan
to pass to your shell command.
Interacting with the Environment: getenv() and
putenv()
Before we leave this discussion, let’s look at how to use environment variables from
within PHP.Two functions serve this purpose: getenv(), which enables you to retrieve
environment variables, and putenv(), which enables you to set environment variables.
Note that the environment we are talking about here is the environment in which PHP
runs on the server.
You can get a list of all PHP’s environment variables by running phpinfo(). Some
are more useful than others; for example,
getenv(“HTTP_REFERER”);
returns the URL of the page from which the user came to the current page.
You can also set environment variables as required with putenv(), as in this example:
$home = “/home/nobody”;
putenv (“ HOME=$home “);
If you are a system administrator and would like to limit which environment variables
programmers can set, you can use the safe_mode_allowed_env_vars directive in
php.ini.When PHP runs in safe mode, users can set only environment variables whose
prefixes are listed in this directive.
Note
If you would like more information about what some of the environment variables represent, you can look
at the CGI specification at http://hoohoo.ncsa.uiuc.edu/cgi/env.html.
Further Reading
Most of the file system functions in PHP map to underlying operating system functions
of the same name.Try reading the man pages for more information if you’re using Unix.
Next
In Chapter 20,“Using Network and Protocol Functions,” you learn to use PHP’s network
and protocol functions to interact with systems other than your own web server.
This again expands the horizons of what you can do with your scripts.