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# exec

(PHP 3, PHP 4 )

exec -- Execute an external program

## Description

string exec ( string command [, array output [, int return_var]])

exec() executes the given `command`, however it does not output anything. It simply returns the last line from the result of the command. If you need to execute a command and have all the data from the command passed directly back without any interference, use the passthru() function.

If the `array` argument is present, then the specified array will be filled with every line of output from the command. Note that if the array already contains some elements, exec() will append to the end of the array. If you do not want the function to append elements, call unset() on the array before passing it to exec().

If the `return_var` argument is present along with the `array` argument, then the return status of the executed command will be written to this variable.

Warning
If you are going to allow data coming from user input to be passed to this function, then you should be using escapeshellarg() or escapeshellcmd() to make sure that users cannot trick the system into executing arbitrary commands.

> Note: If you start a program using this function and want to leave it running in the background, you have to make sure that the output of that program is redirected to a file or some other output stream or else PHP will hang until the execution of the program ends.

See also system(), passthru(), popen(), escapeshellcmd(), and the backtick operator.

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