passthru

The passthru function in PHP is used to execute an external program and display raw output. It's one of the several PHP functions that allow for running system commands, similar to exec and shell_exec, but with some differences in behavior and output handling.

passthru is specifically used when you want to execute a system command that outputs binary data or needs to pass the output directly back to the browser. Unlike exec, which collects the command output and allows you to process it within PHP, passthru sends the output directly to the browser. This makes it suitable for executing commands that produce binary output, like displaying an image or a PDF file.

Like other command execution functions, passthru is vulnerable to command injection attacks. If user-supplied input is incorporated into the command without proper sanitization, it can lead to severe security vulnerabilities.

Since passthru sends output directly to the browser, there is a risk of exposing sensitive information if not carefully handled. A typical use of passthru might be to execute system commands for tasks that require real-time output to be sent to the client, such as streaming video or audio data.

PHP offers other functions for executing external programs, such as exec, shell_exec, and system, each with specific use cases and output handling characteristics.