1. UNIX Shell Dr. Tran, Van Hoai
Faculty of Computer Science and Engineering HCMC Uni. of Technology

2. Where is a shell ? Users Shells & Utilities kernel Hardware C programs
scripts
Users
Shells & Utilities
ksh, bash,
gcc, find
open(), fork(),
Exec(),
kernel
Hardware

3. What is a shell ? To users: And definition A user interface to UNIX
Many shells
Thought harder to use than GUI, but not
Harder to learn
And definition
Program to make the system understand commands (also called command intepreter)

4. Purpose of shell Interactive use Customization of UNIX session
Environment variables
Startup files
Programming
Shell scripts: executing a series of commands

5. Favourite shells GNU Project’s Bash (Bourne-Again SHell) (bash)
Thompson shell → Bourne shell → Bash
Most popular
Command-line editing
Korn shell (ksh)
“Tenex” C shell (tcsh)
C programming style

6. Shell for individual /etc/passwd Default shell for interactive use
hoai:x:556:500:Tran Van Hoai:/home/hoai:/bin/bash
Default shell for interactive use
“which” to find a path of a shell
which tcsh
/usr/bin/tcsh
which bash
/bin/bash
“exec” to change shell
exec bash

7. Interactive use Command history Command-line editing
File/command expansion
Job control

8. Shell scripting Script = set of shell and UNIX commands
Text file
Executable program
Automating repetitive task and administrative tools

9. Simple commands
Sequence of non-blank arguments separated by blanks or tabs
First argument = name of command
ls -l lib.tar.gz
-rwx hoai users :09 lib.tar.gz
command
arguments

10. Types of arguments Options/Flags Parameters -X or –longname
$ tar –c –v –f archive.tar main.c main.h
Options/Flags
-X or –longname
Parameters
Strings, file names
Depends on command

11. Getting help on UNIX “man”: display manual page
Manual entry organization
Commands
System calls
Subroutines
Special files
File format and conventions
Games

12. Security fundamentals
Multiple users identified by a number and and name
hoai:x:556:500:Tran Van Hoai:/home/hoai:/bin/bash
superuser = (id 0, name root)
Set of users can form a group
A user can belong to several groups

13. How are users/groups used?
Used to determine if file or process operations can be performed
Can a given file be read? Written to ?
Can this program be run?
Can I use this piece of hardward?
Can I stop a particular running process?

14. Example hoai@moon:~> ls -l lib.tar.gz
-rwx hoai users :09 lib.tar.gz
read
write
execute

15. Unix file system
is NEXT