Unix I/O Cheatsheet

Overview

• In Unix, everything is a file (devices, kernel, etc.)
• Uniform interface for I/O: open, close, read, write

File Types

• Regular files: Arbitrary data (text or binary)
• Directories: Index for a group of files
• Sockets: For inter-process communication

Directory Hierarchy

• Root directory: "/"
• Absolute pathnames: Start with "/", path from root
• Relative pathnames: Path from current working directory

File Operations

• open: Informs kernel you're ready to access a file
  • Returns file descriptor (int), -1 on error
• close: Informs kernel you're finished accessing a file
  • Important to check return value, especially in threaded programs
• read: Copies bytes from file to memory, updates file position
  • Returns number of bytes read, -1 on error
• write: Copies bytes from memory to file, updates file position
  • Returns number of bytes written, -1 on error

File Metadata

• Per-file metadata maintained by kernel
• Accessed using stat and fstat functions