1. CSC 140: Introduction to IT
UNIX Shells
CIT 140: Introduction to IT

2. CIT 140: Introduction to IT
Objectives
To describe what a UNIX shell is.
To describe briefly some commonly used shells
CIT 140: Introduction to IT

3. CIT 140: Introduction to IT
What is a shell?
A command interpreter.
Runs external commands like cp and rm.
Built-in commands change shell environment:
cd – change directory
VAR=value
I/O redirection.
cat /etc/shells >shells
Ease of use
Command line editing, tab completion, history.
Programming
Conditionals, loops, etc.
CIT 140: Introduction to IT

4. Environment Variables
CIT 140: Introduction to IT

5. Shell Initialization Files
Configure shell settings at login.
Create aliases.
Set environment variables.
bash initialization files
/etc/profile System-wide for sh and bash.
/etc/bashrc System-wide for bash.
~/.bashrc User startup file.
CIT 140: Introduction to IT

6. CIT 140: Introduction to IT
sh/csh Differences
CIT 140: Introduction to IT

7. Which Shell Suits Your Needs?
CIT 140: Introduction to IT

8. CIT 140: Introduction to IT
sh/csh Similarities
CIT 140: Introduction to IT

9. How to change your shell?
Change your login shell.
> chsh zsh
Run the other shell directly
> echo $SHELL
/bin/bash
> zsh %
CIT 140: Introduction to IT

10. CIT 140: Introduction to IT
Shell Metacharacters
Non-alphanumeric characters that have special meaning to the shell.
They cannot be used in shell commands.
Allow you to specify multiple files in multiple directories in one command line.
CIT 140: Introduction to IT

11. CIT 140: Introduction to IT

12. CIT 140: Introduction to IT

13. CIT 140: Introduction to IT
Globbing
?  Matches any one character.
*  Matches zero or more characters.
[]  Matches list of characters inside brackets.
CIT 140: Introduction to IT

14. CIT 140: Introduction to IT
Globbing
> ls *html
announce.html guidelines.html readings.html sites.html
assignments.html index.html schedule.html
> cd assignments
> ls a[2-3]?html
a2.html a3.html
CIT 140: Introduction to IT

15. CIT 140: Introduction to IT
Command History
Up-arrow Previous command
Down-arrow Next command
history List old commands
!! Previous command
!# Command #
!$ Last arg of previous command
CIT 140: Introduction to IT

16. CIT 140: Introduction to IT
Command line editing
Ctrl-a Beginning of line
Ctrl-e End of line
Left-arrow Move back one character
Right-arrow Move forward one character
Ctrl-u Erase line
CIT 140: Introduction to IT

17. CIT 140: Introduction to IT
Filename completion
TAB Completes filename
TAB-TAB Show list of possible
completions.
CIT 140: Introduction to IT