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

448 Chapter 19 Interacting with the File System and the Server
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The exec() function has no direct output. It returns the last line of the result of
the command.
If you pass in a variable as result, you will get back an array of strings representing
each line of the output. If you pass in a variable as return_value, you will get
the return code.
passthru()—The passthru() function has the following prototype:
void passthru (string command [, int return_value])
The passthru() function directly echoes its output through to the browser. (This
functionality is useful if the output is binary—for example, some kind of image
data.) It returns nothing.
The parameters work the same way as exec()’s parameters do.
system()—The system() function has the following prototype:
string system (string command [, int return_value])
The function echoes the output of the command to the browser. It tries to flush
the output after each line (assuming you are running PHP as a server module),
which distinguishes it from passthru(). It returns the last line of the output
(upon success) or false (upon failure).
The parameters work the same way as in the other functions.
Backticks—We mentioned backticks briefly in Chapter 1,“PHP Crash Course.”
They are actually execution operators.
They have no direct output.The result of executing the command is returned as a
string, which can then be echoed or whatever you like.
If you have more complicated needs, you can also use popen(), proc_open(), and
proc_close(), which fork external processes and pipe data to and from them.The last
two of these functions were added at PHP 4.3.
The script shown in Listing 19.5 illustrates how to use each of the four techniques in
an equivalent fashion.
Listing 19.7