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# passthru

(PHP 3, PHP 4, PHP 5)

passthru -- Execute an external program and display raw output

## Description

void passthru ( string command [, int &return_var] )

The passthru() function is similar to the exec() function in that it executes a command. This function should be used in place of exec() or system() when the output from the Unix command is binary data which needs to be passed directly back to the browser. A common use for this is to execute something like the pbmplus utilities that can output an image stream directly. By setting the Content-type to image/gif and then calling a pbmplus program to output a gif, you can create PHP scripts that output images directly.

## Parameters

command

  The command that will be executed.

return_var

  If the return_var argument is present, the return status of the Unix command will be placed here.

## 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

exec()
system()
popen()
escapeshellcmd()
backtick operator

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