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

Using Program Execution Functions
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Creating, Deleting, and Moving Files
You can use the file system functions to create, move, and delete files.
First, and most simply, you can create a file, or change the time it was last modified,
using the touch() function.This function works similarly to the Unix command touch.
The function has the following prototype:
bool touch (string file, [int time [, int atime]])
If the file already exists, its modification time will be changed either to the current time
or the time given in the second parameter if it is specified. If you want to specify this
time, you should give it in timestamp format. If the file doesn’t exist, it will be created.
The access time of the file will also change: by default to the current system time or
alternatively to the timestamp you specify in the optional atime parameter.
You can delete files using the unlink() function. (Note that this function is not
called delete—there is no delete.) You use it like this:
unlink($filename);
You can copy and move files with the copy() and rename() functions, as follows:
copy($source_path, $destination_path);
rename($oldfile, $newfile);
You might have noticed that we used copy() in Listing 19.2.
The rename() function does double duty as a function to move files from place to place
because PHP doesn’t have a move function.Whether you can move files from file system to
file system and whether files are overwritten when rename() is used are operating system
dependent, so check the effects on your server.Also, be careful about the path you use to
the filename. If relative, this will be relative to the location of the script, not the original file.
Using Program Execution Functions
Let’s move away from the file system functions now and look at the functions available
for running commands on the server.
These functions are useful when you want to provide a web-based front end to an
existing command-line–based system. For example, you previously used these commands
to set up a front end for the mailing list manager ezmlm.You will use them again when
you come to the case studies later in this book.
You can use four main techniques to execute a command on the web server.They are
all relatively similar, but there are some minor differences:
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exec()—The exec() function has the following prototype:
string exec (string command [, array &result [, int &return_value]])
You pass in the command that you would like executed, as in this example:
exec(“ls -la”);