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# exec

(PHP 3, PHP 4, PHP 5)

exec -- Execute an external program

## Description

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

exec() executes the given command.

## Parameters

command

  The command that will be executed.

output

  If the output argument is present, then the specified array will be filled with every line of output from the command. Trailing whitespace, such as \n, is not included in this array. 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().

return_var

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

## Return Values

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.

To get the output of the executed command, be sure to set and use the output parameter.

## Examples

Example 1. An exec() example
`<?php // outputs the username that owns the running php/httpd process // (on a system with the "whoami" executable in the path) echo exec('whoami'); ?>`

## Notes

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.

> Note: When safe mode is enabled, you can only execute executables within the safe_mode_exec_dir. For practical reasons it is currently not allowed to have .. components in the path to the executable.

Warning
With safe mode enabled, the command string is escaped with escapeshellcmd(). Thus, echo y | echo x becomes echo y \| echo x.

## See Also

system()
passthru()
escapeshellcmd()
pcntl_exec()
system()
backtick operator

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