# System program execution

- Introduction
- Installing/Configuring
  - Requirements
  - Installation
  - Runtime Configuration
  - Resource Types
- Predefined Constants
- Program execution Functions
  - escapeshellarg — Escape a string to be used as a shell argument
  - escapeshellcmd — Escape shell metacharacters
  - exec — Execute an external program
  - passthru — Execute an external program and display raw output
  - proc_close — Close a process opened by proc_open and return the exit code of that process
  - proc_get_status — Get information about a process opened by proc_open
  - proc_nice — Change the priority of the current process
  - proc_open — Execute a command and open file pointers for input/output
  - proc_terminate — Kills a process opened by proc_open
  - shell_exec — Execute command via shell and return the complete output as a string
  - system — Execute an external program and display the output