Shell#

Overview#

A shell is a command-line interface (CLI) that mediates between the user and the OS kernel. It accepts commands, executes programs, and manages I/O streams.

Terminology:

  • Terminal: Interface for interacting with a shell
  • Console: Physical or virtual text display (historically distinct from terminal windows)

Terminal Emulators#

A terminal emulator provides a GUI-based environment to run shell sessions.

Examples:

  • GNOME Terminal
  • iTerm2
  • Windows Terminal

Characteristics#

  • Emulates legacy text terminals
  • Supports multiple sessions (tabs/panes)
  • Provides access to CLI tools within a GUI

Shell#

The shell is the command interpreter responsible for:

  • Parsing user input
  • Executing commands/programs
  • Managing processes and I/O redirection

Common Shells#

Shell Description
Bash Default on most Linux systems; GNU project
Zsh Extended Bash with improved UX/features
Fish User-friendly, modern shell
KornShell Advanced scripting capabilities
Tcsh C-shell derivative

Mental Model#

  • Terminal emulator = interface
  • Shell = interpreter
  • Kernel = execution layer
User -> Terminal -> Shell -> Kernel -> Hardware
Backward Permissions Shell Prompt Forward