CS 307: UNIX PROGRAMMING ENVIRONMENT INTRODUCTION TO SHELLS, COMMANDS, MAN PAGES, TEXT EDITORS, AND COMPILERS Prof. Michael J. Reale Fall 2014
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CS 307: UNIX PROGRAMMING
ENVIRONMENT
INTRODUCTION TO SHELLS,
COMMANDS, MAN PAGES,
TEXT EDITORS, AND COMPILERS
Prof. Michael J. Reale
Fall 2014
“If you hold a Unix shell to your ear, can you
hear the C?”
-- A venerable yet bad Unix joke
Introduction to Shells
What is a “Shell”?
When you login to a Unix system with your
username and password, the OS starts a program
called a “shell”
What is a “Shell”?
Shell – program that allows user to:
Enter commands and run programs
Redirect input and output
Program/script in shell itself
“Shell scripts” – list of commands to shell
Effectively an interpreted programming language with
variables and control flow (i.e., loops, if-else statements, etc.)
Shell / Kernel / User Relationship
Kernel:
Creates shell
Connects user to shell
Provides services and exposes resources to programs
(including the shell)
Disposes of shell when user is done
Shell / Kernel / User Relationship
Lineage of Unix Shells:
Thompson’s Shell
Thompson’s shell
Used until 6th ed. Unix
First Unix shell
Split into the Bourne Shell (sh) and C-Shell (csh)
Lineage of Unix Shells:
Thompson’s Bourne (sh)
Bourne shell (sh)
Default in 7th ed. Unix
Written by Stephen Bourne at Bell Labs to replace original
shell and to add new features (like scripting)
Still included in many distributions of Unix/Linux (/bin/sh)
Pretty primitive by today’s standards
Lineage of Unix Shells:
Bourne (sh) korn
Korn (ksh)
Written by David Korn at Bell Labs
Heavy focus on shell programming
Improvement over Bourne (sh) and adds some features from
C-shell (csh)
Popular among commercial users
Adopted in future editions of AT&T Unix (8-10th
editions)
Was proprietary until year 2000
http://www.kornshell.com/
Lineage of Unix Shells:
Bourne (sh) Bourne Again (bash)
Bourne Again (bash)
Originally written by Brian Fox at Free Software
Foundation (FSF)
Part of GNU Toolkit
Free replacement for Bash (sh), hence the pun
Community supported
http://www.gnu.org/software/bash/
Lineage of Unix Shells:
Thompson’s C-Shell (csh)
C-Shell (csh)
Written by Bill Joy as part of BSD
Based on C Programming language.
Scripting commands are based on C statements.
Under BSD License, so couldn't distribute freely
Lineage of Unix Shells:
C-Shell (csh) TCSH
TCSH (tcsh)
Enhancement of the C-shell while being free from
licenses
In public domain for academic users
Lineage of Unix Shells: Family Tree
http://web.cs.sunyit.edu/~merantn/cs307/img/shells.jpg
Shells: Who Uses What?
Split by users:
Bash Linux
Tcsh BSD
Korn Commercial users
Depends on primary use:
Interactive use: bash or tcsh
Scripting: Bourne (portability/compatibility) or Bash (extended features)
Shells: What shells do I have?
See available shells on your system:
cat /etc/shells
Can switch to a different shell by calling it as a program:
/bin/bash
You can write your own shell (it’s a garden-variety program).
Shell Customization
Can customize your shell (what programs start, what
variables are set, etc.)
Usually a default file in the system, but also one in
your home directory
Bourne (sh) Customization
Bourne (sh) uses ~/.profile
May also have system-wide file /etc/profile, which is
executed before local .profile
Note: sometimes sh actually linked to bash
http://stefaanlippens.net/bashrc_and_others
Bash Customization
For login bash shells:
Reads and executes /etc/profile (system-wide)
Looks for one of these (in this order) and reads first one it
finds:
~/.bash_profile
~/.bash_login
~/.profile
Reads and executes ~/.bash_logout on logout (if it exists)
https://www.gnu.org/software/bash/manual/html_node/Bash-Startup-Files.html
Bash Customization
For interactive, non-login bash shells:
~/.bashrc
Executed when you call bash manually (/bin/bash) or
open a new terminal window (xterm)
C-Shell Family Customization
C-shell and its descendants run the following:
.cshrc Shell environment
Run on both interactive and non-interactive shells
.login Run on login
Contains commands and variables
.logout Script that runs on logout
Basic Command Syntax
How to enter commands
To run a command, type it at the shell prompt and
hit Enter:
Example: ls
Lists the contents of the current directory
Command Syntax
Commands usually have the following general
syntax:
Command_name options arguments
(Whitespace separates each part)
Command Syntax
Command_name = the command/program we wish to execute
Options = determine how the program/command is run
Example: ls -a Lists ALL the contents of current directory, including hidden files (i.e., files with
a period before their names)
Arguments = provide additional information to the command, such as filenames
Example: ls /etc List the contents of the /etc directory (instead of the current one)
Options and Arguments
Options may be combined:
Example: ls -al
List ALL the contents AND list it in the “long” format (-l)
Options may also have arguments (known as “option arguments”)
Example: cal –B 2
Usually, cal just shows the current calendar month
-B 2 shows the current month AND the two months before it
“2” is the option argument for option “-B”
http://tldp.org/LDP/abs/html/special-chars.html
Long Options
Long options use a double-dash --
Example: less --version
Prints the version information for the program less
Previous Commands
Up arrow on keyboard access previous
commands
Type first two letters then UP search command
history
Grouping and Stopping Commands
Group commands with a semicolon ;
Example: cd ; ls
Go to home directory and then list contents
Stop commands with CTRL-C
Interrupt; break out of whatever you are doing
Common Signals
Sequence Action
^A Move cursor to start of line
^E Move cursor to end of line
^C Interrupt. Break out of what you're doing
^D eof. End of transmission, end of file
^U Erase entire input line
^L Clear screen above current line
^TDisplay status of foreground process
(FreeBSD)
Can use Control-letter to send signals to the terminal
Typically abbreviated with ^
Example: CTRL-C or ^C
COMMAND KATA 0
Command Kata 0: Preparation
First, go to ~/cs307
Command Kata 0
Where am I? pwd
Create directory kata mkdir kata
What is in my current location? ls
Go to directory kata cd kata
Where am I? pwd
Go to parent directory cd ..
Where am I? pwd
Remove directory kata rmdir kata
What is in my current location? ls
R.T.F.M. = “READ THE (Fine) MANUAL!!!”
MAN PAGES (DOCUMENTATION)
MAN Pages
MAN pages
The MANual pages
Documentation for the Unix system and programs
Usage: man [section] command
Example: man ls
Brings up documentation for ls command
See Hahn chapter 9
How to navigate in MAN pages
Navigation: Hahn page 195
Moving:
Down page space, f
Up page b
Up/down line up/down arrows
Search:
Down /
Up ?
Next match n
How to navigate in MAN pages
Jump to:
Top of page g
Bottom of page G
Quit q
Help h
MAN Page Organization
Synopsis = Overview of the command, listing options and requirements
Optional items are contained within [brackets]
Description = Description of actions performed by the command and detail information about all of the supported options
Examples = Examples of common usage
See Also = Other man pages to read for related information
MAN Search
man -k keyword - search the man pages
MAN Sections
Manual sections:
1 - Commands
2 - System Calls
3 - Library Functions
4 - Special Files
5 - File Formats
6 - Games
7 - Misc Info
8 - System administration
COMMAND KATA 1
Command Kata 1: Preparation
First, go to ~/cs307
Create directory kata1 and go to it:
mkdir kata1; cd kata1
Command Kata 1
Create file abc touch abc
What is in this folder? ls
Copy abc to def cp abc def
What is in this folder? ls
Rename abc to ghi mv abc ghi
What is in this folder? ls
Remove def and ghi files rm def ghi
What is in this folder? ls
Text Editors
Common Text Editors
pico
Simple text editor written by the University of
Washington to accompany their mail client, pine.
nano
A GNU pico clone with enhancements.
Common Text Editors
vi
Original UNIX text editor
Not as easy to use as pico/nano, but much more powerful.
More information: Run vimtutor
Back page of UNIX Command summary handout (see website)
UNIX in a Nutshell Book
vim
vi Improved
Basic Compiler Usage
GNU C/C++ Compiler
gcc & g++
gcc compiling C code
g++ compile C++ code
Source code file extensions must either be .c or .cpp
gcc/g++ Usage Example
Usage:
gcc [ -o outfile ] source
Example:
gcc -o name_of_executable source.c
OR
g++ -o name_of_executable source.cpp
WHERE
name_of_executable = executable file to create after compiling your source code, instead of using the default a.out
Basic Compiler Usage:
Hello World with gcc/g++
Let do a simple exercise to:
Compile a simple program in C/C++
Get more practice editing text files
Basic Compiler Usage:
Hello World with gcc/g++
Make a folder called “hello” in your home directory and go there:
mkdir ~/cs307/hello; cd hello
Open vi:
vi hello.cpp
(This will create hello.cpp if it does not exist)
Press ‘i’ to enter insert mode
Basic Compiler Usage:
Hello World with gcc/g++
Type:
#include <iostream> using namespace std; int main() {
cout << "Hello World!" << endl; return 0;
}
Hit “ESC” a couple of times, then type SHIFT+Z twice (save and exit)
Basic Compiler Usage:
Hello World with gcc/g++
Compile the source file:
g++ -o hello hello.cpp
Run program!
./hello
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