CSCI 1730 - Week 09 Topics

CSCI 1730 - Week 09 Topics Overview

• Systems Programming Overview (continued)
• File I/O

User UNIX Interface: SHELL

• Command line interface between user and system.
• Automatically starts upon login.
• Enables the execution of other programs.
• Supports a command language for commands, programming, and shell scripting.
• Offers variables, loops, conditionals, etc.
• Processes user commands and may call system calls to complete operations.

Various UNIX Shells

• Common UNIX shells:
  • bash: Default shell used (e.g., in Odin).
  • sh: Bourne shell.
  • ksh: Korn shell.
  • csh: C shell.
  • zsh: Z Shell.
• Differences primarily related to scripting and aliasing.
• Example bash command:
  • for i in {1..10}; do echo $i; done (not compatible with csh).

Environment Variables

• Consists of variables used by the shell for operations:
  • Variable Structure: Name and Value.
• View current list with env command.
• To display a specific variable's value, use: echo $<var_name>.
• Notable variables:
  • HOME: User's home directory.
  • PATH: Executable search path.
  • USER: Current user.
  • HOSTNAME: System hostname.
  • PWD: Current working directory.

Setting Environment Variables

• Setting a variable uses:
  • For bash/ksh: <name>=<value>.
  • For tcsh: setenv <name> <value>.
• Examples:
  • PS1=myprompt>: Custom prompt.
  • PATH=$PATH:$HOME: Appending home to PATH.
  • DATE=$(date): Store current date time.

Aliases

• Provides shorthand for frequently used commands:
  • Syntax:
  • For ksh/bash: alias <shortcut>=<command>.
  • For tcsh: alias <shortcut> <command>.
  • Examples:
  • `alias ll=