CIS 14A - Operating Systems (UNIX)

1
CIS 14A - Operating Systems(UNIX)

• Markus Geissler, MBA
• Nghiep Nguyen, MSEE

2
About the Instructor...

• Nghiep Nguyen, MSEE-Sacramento High School,
  1983- AA in Math and Science Sacramento City
  College, 1985-BS in Electrical Electronics
  Engineering
• UC Davis, 1987
• -MS in Electrical Electronics Engineering
• CSUS, 1993

3
Experience

• - Electronic Engineer, 87 - 90
• Sacramento Army Depot
• Write Test Program Sets for Unit Under Test for
  Tomahawk Computer.
• - Software Engineer, 90 - 95
• McClellan Air Force Base
• Operational Flight Program for A-10

4
Experience

• - Electronic Engineer, 95 -96
• Tinker Air Force Base
• B-2 Stealth Bomber
• - Software Engineer, 96 - 98
• McClellan Air Force Base
• A-10 aircraft

5
Experience

• - Associate Programmer 1/98 - 10/98
• P.O.S.T Work with PowerBuilder, SQL
• - Associate Systems Software 10 - 11/98
• F.T.B Sybase DBA
• - Systems Software Specialist, 11/98 to Present
• Legislative Data Center
• Unix (Sun Solaris) System Administrator

6
Experience

• Adjunct Faculty 8/97 to Present
• Cosumnes River College
• Unix, Internet, HTML
• Java, Visual Basic
• Visitor Lecturer 8/02 6/03
• California State University, Sacramento
• Visual Basic, Java

7
Office Hours

• None
• E-mail nghiep_nguyen_at_yahoo.com
• Work nghiep.nguyen_at_lc.ca.gov
• Web site http//www.geocities.com/nghiep_nguyen

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Textbook(s)

• Required
• UNIX System V - A Practical Guide (Third Edition)
• by Mark G. Sobell
• Addison-Wesley Publishing Company
• Strongly recommended
• CIS 14A Lecture Slides
• By Markus Geissler
• Download from website

9
Reverse Flows of Knowledge

• Examinations
• Hands-on in Classroom
• One make-up exam per person at the instructors
  convenience
• No more than 90 possible on makeup exams
• Homework projects

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Other Resources

• UNIX Utility Program Reference
• Back of textbook (starting on p. 521)

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Things You Should Know Before Starting This Course

• A basic understanding of the components of a
  computer system
• CIS 1

12
UNIX

• What exactly is UNIX?
• Computer Operating System
• large set of utility programs
• general user
• programmer
• communication
• administrative commands

13
Operating System

• DefinitionAn operating system (OS) is a set of
  instructions that manages all computer operations
  and provides an interface between user(s) and
  system resources.

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UNIX

• Computer operating system (OS)
• Large set of utility programs
• Based on C programming language
• Used in enterprise networks

15
What Can UNIX Do For You?

• General user applications
• Programming environment
• Typesetting tasks
• Communication applications
• Administration commands

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The Inner Workings of a Computer - Summary

• Central Processing Unit
• Memory
• Storage
• I/O

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Central Processing Unit (CPU)

• Brain of the computer
• Executes instructions from programs and processes
• Manufacturers include
• Intel
• Advanced Micro Devices (AMD)
• Cyrix
• Motorola
• Sun Microsystems

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Memory

• RAM (Random Access Memory)
• Volatile
• Information disappears when electrical power to
  RAM is interrupted
• Capacity measured in Megabytes (MB)
• Access speed measured in Nanoseconds (ns)
• Holds data before and after CPU processes them
• Program instructions
• Application data

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Storage

• Hard disk
• Installed inside computers case
• Floppy/ZIP/JAZ/SyQuest disks
• Portable require disk drive
• Disks are typically non-volatile
• Data called into memory when needed
• Capacity measured in Gigabytes (GB)
• Magnetic Tape
• Largely used for data backup

20
Input/Output (I/O)

• Reads input from a device into memory
• Keyboard
• Mouse
• Writes output from memory to devices
• Monitor
• Printer
• Disk drives are input and output devices
• long term storage devices

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UNIX Facts

• Created in 1969
• by Kent Thompson
• Based on C language
• ATT (Bell Labs) shared UNIX with colleges and
  universities
• Colleges made enhancements
• Berkeley Software Distribution (BSD)
• See Introduction to UNIX
• by Fiamingo, DeBula and Condron

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Linux

• Compact version of UNIX for PC
• Created by Linus Thorvald
• Not yet standardized
• Supported by a large, active user community
• Free versions available on the Internet
• approx. 50 for RedHat Linux

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Major UNIX Components

• Kernel
• Shell
• File System

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Kernel

• Core of UNIX OS
• Manages hardware, memory and file system
  resources
• Controls transmission of information between user
  application and CPU
• Stores information about the arrangement of the
  computer system and the network

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Shell

• Interface between user and OS
• Korn shell
• Most robust features
• Bourne shell
• Subset of Korn shell
• C shell
• Not related to other two shells
• Most widely used in SunOS

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UNIX OS Components

• Shell
• Shell program are interpreted, not compiled
• commands are read and executed one by one
• compiled program is read and converted to a
  machine language then execute all at once
• slower than compiled language such as C
• Three types of Shells Korn, Bourne, and C

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Shell History

• Bourn -- Steve Bourne at ATT Bell Labs
• Original UNIX shell -- compactness speed
• lack features for interactive use
• C -- Bill Joy (SUNW)
• friendly features for users
• larger and slower than Bourne
• Korn -- David Korn of ATT Bell Labs
• faster than C shell, will run Bourne Script

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File System

• Organizes data on disk in a hierarchical
  structure of directories
• File
• Program or data
• Directory/folder
• Similar to file drawer
• Each disk has root directory
• Subdirectory
• Directory/folder within other directory

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File System Structure

• Root (/)
• /etc system administration files
• /usr executable commands, s.a. utilities
• /opt third-party software
• /export/home or /home users home directory

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Multitasking OS

• Used to approach 100 of computer resource
  utilization while increase user productivity
• Reduced cost per user
• Time slicing
• Users can run multiple processes
• Increases user productivity
• UNIX refers to task as process
• Usually maximum of 25 concurrent processes per
  user session

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Multi-User OS

• Supports 1 - 2000 users
• Users share system resources
• To approach 100 percent in computer resource
  utilization while reducing the cost per user
• Share system resources

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Interactive Mode

• Immediate response to keyboard or mouse input
• No news is good news
• Display returns shell prompt after commands are
  issued
• Different shells have different prompts
• Detailed feedback only when errors made

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Networking Terms

• Host - a computer system
• Host Name - a unique name for a system
• IP address - a number used by networking
• Network
• connects machines to enable comm. between users
  on other systems.
• Server provides resources to one or more clients
  on the network

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More Terms

• Client is a machine that uses services from one
  or more servers on a network
• NFS (Network File System) enables files to be
  shared across the network.
• NIS (Network Information Services) enables system
  administration functions to be centralized on a
  server.
• Client-Server

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Network

• Connects computers to enable communication
  between users on multiple systems

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Clients vs. Servers

• Server
• Provides resources to one or more clients on the
  network
• Usually requires more powerful equipment than
  clients
• Client
• Computer that uses services from one or more
  servers
• Front end vs. back end

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Set Up

• User Account
• must have it set up before a user can log in
• contains essential user account info
• User name identifies a user to the system
• is created by System Administrator.
• Bring your class registration/schedule to the
  computer lab. The lab assistant will set up the
  Unix account for you

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Logging into CRCs LAN

• Login name
• First four letters of your last name
• Last four digits of student ID number
• Initial password new2lan
• Change password right away

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Password Security

• Do not choose a password that can be related to
  you!
• Use a password that does not resemble a word in
  the dictionary
• Case sensitivity

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Password Guidelines

• No less than six characters
• Must contain at least two alphabetic characters
  and at one numeric or special character
• can have spaces, avoid special characters
• Cannot be login name or reverse
• New password must differ from old password by at
  least three characters

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Accessing CRCs UNIX Box

• From Windows 95 or Windows NT
• Connect to Internet via your ISP
• Start, Run
• TELNET 165.196.137.125orTELNET
  cosumn.crc.losrios.cc.ca.us

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User Account

• Required for user login
• Identifies user to the system
• Contains essential user account info
• Special environment settings for user
• Mail file

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Logging into CRCs UNIX Box

• Log into system
• Initial username is same as for CRCs LAN
• Initial password new2mini
• Password will not display when typed
• Connection times out if you take too long
• Use exit command at the prompt to log out
• Also possible to disconnect within TELNET
  application

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Entering UNIX Commands

• Type commands with keyboard
• To correct a typing error, use Delete key
• NOT the Backspace key
• Press Enter key to send command to kernel

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Changing Your Password

• Use passwd command at prompt to change your
  password
• Type old password first
• Type new password twice
• Password will not be displayed when typed
• Password has to have at least one number in it
• Suggestion Use same password as LAN account and
  add a number, if necessary

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Getting Help in UNIX

• Use man command
• Include command about which you want help
• man ls
• Use man ls more to display one page at a time
• Pipe character
• Use Ctrl-C to interrupt file display
• If file is too long for one screen

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Logging a TELNET Session

• Record all activity within a session
• In TELNET utility
• Choose Terminal, Start Logging
• Specify filename to which to log
• Local drive
• Network drive (U drive in CRC lab)
• Up to 5 MB of space
• Choose Terminal, Stop Logging to stop writing to
  log file

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The script Command

• Logs commands entered and results displayed
• If no filename specified, script logs to file
  typescript
• Type exit to stop logging and close the log file

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Printing Log Files

• Type lp filename to print to CRC lab
• FTP file to home computer and print to local
  printer
• Printing from DOS Editor may be easier than from
  Notepad
• Potential problems with line breaks
• Turn off Word Wrap

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UNIX Commands

• Command line format
• command - option(s) argument(s)
• Options modify the command
• Arguments tell the computer to what to apply the
  command
• Example
• cd directory_name
• ls aFIR pathname

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Command Syntax

• Command Line Format
• command option(s) argument(s)
• case sensitive
• blank space does matter since it is the delimiter
  for the shell
• do not necessary require all three parts
• 256 characters can be entered on a single command
  line

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Commands

• passwd
• ls
• cd
• pwd
• cp
• rm
• mv

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Commands

• cat
• more
• man
• mkdir
• rmdir
• date
• echo

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Commands

• cal
• head
• tail
• wc
• grep
• find

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Commands

• cd directory_name
• pwd
• ls -aFlRt pathname
• man command

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Commands

• pwd -- present working directory
• cd -- change directory
• mkdir -- create a new directory
• ls -- diplays contents of your directory
• l -- stands for long information
• F -- File type option
• a -- display all files (including customization
  files)
• R -- display recursively all directories/sub-direc
  tories and their corresponding files

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Commands

• ls -F will display the following symbols next the
  listing of files
• / for directory
• executable file, shell script
• _at_ symbolic link
• none text file (ASCII)

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Commands

• rmdir - remove directory
• head -n --- displays the first n lines
• tail -n -- displays the last n lines
• wc -- word count command to display numbers of
  lines, words, characters
• diff -- to display the differences between two
  files.

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Commands

• grep -- search for a pattern in a file or files

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The cal Command

• Displays a calendar on the screen
• Syntax cal month year
• Month from 1-12
• Year from 1 to 9999 (!)
• Example cal 1999
• Displays the calendar for 1999
• Eastern and Western calendars were combined in
  1752
• Check out September 1752!

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The who Command

• Lists current system users
• Syntax who
• Example who sort -r
• Sorts users in reverse order
• Example who grep geisslm
• Allows you to check whether or not user geisslm
  is logged-in
• More details on examples later

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Directory Structure
/
/dev
/usr
/bin
/home
/cis14a
/user A
/user B
/home
63
Path

• Absolute path
• Type pwd at prompt
• Present working directory
• /usr/cis14a/user B/home
• To change to directory, typecd /usr/cis14a/user
  B/home
• Relative path
• From /usr/cis14a/user B directory, typecd home

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File Path

• absolute path -- Starts with / (stands for root
  directory) and go to where you want to go
• relative path -- start from where you are and
  move to sub-directory or parent directory

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The cd Command

• Navigate directory structure
• Type cd .. at prompt to change to parent
  directory
• Directory above current directory
• Type cd without attributes to change to home
  directory

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Special Directory Names

• . represents current directory
• .. represents parent directory
• Above current directory in directory tree
• Combine .. and sibling subdirectory name to
  move to sibling subdirectory
• To change from /usr/cis14a/user B directory to
  /usr/cis14a/user A, typecd ../user A

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The ls Command

• List the contents of current directory
• Type ls at prompt
• Directory entry types
• - (hyphen) for file
• d for directory

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ls Command Options

• Directory entry type
• User/group/other (world) permissions
• Number of links
• Owner name
• Owner group
• File size in bytes/blocks
• Date of file creation/last access
• Filename/directory name

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ls Command Options

• ls -l lists details about contents
• Long version
• ls -F shows slash (/) after directory name
  listing
• ls -R lists contents of entire tree (including
  subdirectories)
• Recursive

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More ls Command Options

• ls -r lists contents in reverse order
• ls -l (filenames) to list specific files
• ls -a displays all contents, including hidden
• ls -s lists size of file/directory in blocks
• 1 block 512 bytes
• ls -i displays systems item number for each
  directory entry

71
More ls Command Options

• ls directory name lists contents of other
  directory

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Combining ls Command Options

• Possible to combine ls command options
• ls -a -F is the same as
• ls -aF
• more option
• Say pipe more
• Lists one screen at a time
• Example ls -R more
• More on piping later

73
UNIX Filenames

• At least one character long
• Maximum length 255 characters
• Case-sensitive!
• Uppercase and lowercase characters are distinct
• Unlike DOS or Windows 9x

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Special Characters in UNIX

• Filenames cannot contain certain special
  characters
• Special meaning to the shell
• Examples
• ? ( ) lt gt / \
• see p. 38 in Sobell textbook for list

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UNIX Wildcards

• Wildcards replace characters
• replaces zero, one or more characters
• ? replaces one character
• match one of the choices inside brackets
• match each of the choices inside braces
• Example ls ?he
• Returns ah123e, bhe, 1h23e, etc.
• Example ls taeiou1-3p
• Returns tap, tep, tip, top, tup, t1p, t2p, t3p

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Creating a Directory

• Type mkdir command at prompt
• Example mkdir reports
• Possible to create multiple directories with one
  command
• Use space as delimiter
• Example mkdir memos letters

77
Clearing the Screen

• Use clear or cls command to clear screen
• Clears screen buffer
• prompt only will appear at top of screen

78
More mkdir Command Options

• mkdir -p cis14a/hw1
• Creates cis14a directory as well as hw1
  subdirectory below cis14a directory
• Use -p option to create multiple subdirectories
  at multiple levels at the same time
• Example mkdir -p cis14a/hw2 cis14b

79
The rmdir and rm Commands

• Use rmdir to remove a directory
• Current directory must be parent of directory to
  be deleted unless absolute or other relative path
  is specified
• If directory is not empty, use rm command
• rm -r hw1 for recursive remove
• rm -ir hw1 for interactive recursive remove
• System will prompt for confirmation

80
The cat and more Commands

• cat filename
• Displays contents of file
• more filename
• Displays contents of file in segments
• Press Enter key to display one line at a time
• Press Spacebar to display one screen at a time
• Similar to pg filename

81
Ctrl Commands

• Ctrl-c interrupts current activity
• Ctrl-u erases current command line
• Ctrl-w erases word in current command line
• Ctrl-s stops scrolling screen output
• Ctrl-q restarts scrolling screen output
• Other commands can be customized for user by
  administrator

82
The head and tail Commands

• head -n filename
• Displays top portion of file
• head -5 hw1 displays first 5 lines of file hw1
• tail -n filename
• Displays bottom portion of file
• tail -10 mbox displays last 10 lines of file mbox

83
UNIX Editors

• Use editor to create and edit files
• Several editors available
• vi - most commonly used
• pico - not included in SVR4
• Not available at CRC
• emacs - not included in SVR4
• Not available at CRC

84
Visual Editor (vi)

• Type vi at prompt to start editor
• vi filename to edit existing file (p. 212)
• Three modes (p. 183)
• Command mode
• Hit Esc key to access command mode
• Input (Text) mode
• Last-line mode (shiftcolon keys)

85
Accessing vis Insert Mode

• From command prompt, press
• i to insert text before cursor
• I to insert text at beginning of line
• a to append text after cursor
• A to append text at end of line
• o to open new line below cursor
• O to open new line above cursor
• Page 214

86
Accessing vis Last-Line Mode

• From command mode, press (colon)
• Necessary to save file and exit vi

87
vi Cursor Movements

• Command mode
• j or ? moves cursor down one line
• k or ? moves cursor up one line
• l or ? moves cursor to the right
• h or ? moves cursor to the left
• Ctrl-D moves down one half screen
• Ctrl-U moves up one half screen
• Ctrl-F moves forward one screen
• Ctrl-B moves backward one screen

88
More vi Cursor Movements

• Command mode
• w moves to next word
• moves to end of line
• G moves to last line
• Many more...

89
vi Commands

• dd - delete one line to buffer
• ndd - delete n lines
• x - delete one character
• dw - delete one word to buffer
• d - delete to end of line to buffer
• d0 - delete to beginning of line to buffer

90
Command Mode

• u -- undo a last command/change
• . -- do last change again
• Copy Text
• yy - yank a copy of a line to buffer
• nyy - yank a copy of n line to buffer
• yw - yank a copy of a word to buffer
• Past Text
• p -- put buffer after a cursor
• P -- put buffer before a cursor

91
Command Mode

• cw -- change a word
• ncw -- change n words
• c -- change to end of a line
• r -- replace one character
• R -- replace the text (type over)

92
Last-Line Mode Commands

• set showmode indicates Insert Mode or Command
  Mode
• At bottom right of screen
• set nu displays line numbers
• set nonu turns off line number display
• set list displays invisible characters
• set ic specifies that pattern search should
  ignore case

93
Searching File Contents

• Access vis command mode
• /string finds next occurrence of string
• /string searches for string at the beginning
  of a line
• /\gtstring searches for string at end of word
• More examples on p. 197 of textbook

94
Last - line Mode

• To turn off an option, put a no infront of the
  variable, i.e.,
• set nu
• set nonu -- to turn it off
• Search for text
• /text -- go forward to the first occurence of
  text
• ?text -- go backward to previous occurence of
  test

95
Moving and Deleting Lines

• 3,8d deletes lines 3 to 8
• 4,9m 12 moves lines 4-9 to line 12
• 2,5t 13 copies lines 2-5 to line 13
• 5,9w filename writes lines 5-9 to filename

96
File Management Summary

• Copying
• Renaming
• Moving

97
The cp Command

• Create an exact copy of another file
• With the same name in a different directory
• Possible to specify target directory only
• With a different name in the same directory
• Syntax cp source target
• Example cp misc ./w1/misc
• Copies file misc to subfolder w1 with the same
  name

98
More About the cp Command

• Example cp w2/ w4
• Copies all files from w2 directory to w4
  directory
• Does NOT copy subdirectories under w2
• cp -r w2/ w4 also copies subdirectories
• Recursive
• Lowercase R!

99
Copying Multiple Files

• Example cp test test.out w3
• Copies files test and test.out to w3 directory
• w3 directory must exist

100
The mv Command

• Moves and/or renames a file
• Original file will disappear
• Different from cp command
• Example mv test exam
• Renames file test to file exam
• Example mv exam w4
• Moves file exam to directory w4
• w4 directory must exist
• mv command will not create it

101
Commands For Analyzing And Manipulating Files

• sort - sort file contents
• grep - search file for a pattern
• diff - point out differences between files
• comm - details file differences
• wc - counts words, lines and letters in file
• compress - reduce file size to conserve disk space

102
The sort Command

• Sort information within files and/or merge
  different files
• Example sort filename
• Sorts filename alphabetically by first word
• Example sort -f 2 filename
• Sorts filename alphabetically by third word
  while ignoring case-sensitivity

103
The grep Command

• Global regular expression pattern
• Find text patterns in files
• Syntax grep options pattern filelist
• Example grep echo test1
• Finds pattern echo in file test1 and displays
  lines matching pattern

104
More grep Command Examples

• Example grep -c echo test1
• Displays line count of lines matching pattern
• Example grep -l echo
• Displays name of file that contains one or more
  matches

105
The diff Command

• Shows lines that are different between two files
• Syntax diff filename1 filename2
• Example diff t1 t2
• Lists line and column number
• Lists different text patterns

106
The comm Command

• Displays line-by-line comparison of sorted files
• Files must be sorted!
• Syntax comm filename filename
• Example comm file1 file2
• Results displayed in three columns
• file1 unique text patterns
• file2 unique text patterns
• common text patterns

107
The wc Command

• Word Count
• Display number of
• Lines
• Words
• Characters
• Syntax wc options file-list
• Example wc -lw memo
• Displays the number of lines and words contained
  in the file memo

108
The compress Command

• Compresses files to reduce amount of space
  required on disk
• Similar to ZIP utility in DOS/Windows
• Compressed file cannot be viewed/executed until
  decompressed
• Syntax compress filename
• Results in file filename.Z
• Example compress -v text
• -v option displays compression ratio

109
Limiting Access to Resources

• Use permissions
• Not available in DOS
• Usually available only on network operating
  systems (NOS)
• Who can change permissions?
• Owner of file or directory
• Administrator

110
Cis-14A Misc

• Printing
• lp (after using script command)
• File Transfer Protocol (FTP)
• Open Dos Command window
• ftp 165.196.137.125 to log in
• Telnet Preference menu
• Name your file, and location
• start logging, do work, and stop logging
• Use word processor to print your file

111
Cis-14A Misc

• Turn in assignments 1 and 2
• File Structure
• Tree structure
• Directory, and Files
• File names
• Extension
• Absolute and Relative Path
• cd, mkdir, rmdir, rm, cp, mv
• Midterm 1

112
File Structure

• Pyramid structure, inverted tree
• Each directory -- a subject
• a folder
• can be divided into smaller directories for more
  clarity or easy to use
• sub-directory(ies) and/or file(s)
• the end of a path

113
File Structure

• File Name
• 14 chars, some has up to 255 chars
• A-Z, a-z
• 0 - 9
• underscore (_)
• period (.)
• comma(,)

114
File Structure

• Filename Extension
• usually after period (filename.ext)
• can use more than one period
• meaningful
• .ext, .c, .txt, .990206
• Invisible Filename
• start with a period (.filename)
• ls -a

115
File Structure

• Absolute and Relative Paths
• Commands that work with directory
• Change or go
• create, delete
• rename
• copy
• empty, or non-empty

116
File Structure

• Standard Unix Directories / -- root
• /home, /export/home
• /usr -- system information
• /usr/bin
• /usr/sbin
• /etc
• /var -- files that vary as system runs
• /tmp
• /dev

117
File Structure

• File or Directory Permission
• r read from the file
• w write to the file
• x execute the file
• ls -l

118
File Structure

• chmod mode filename
• mode
• who
• op
• permission
• File owner or root can change permission of a file

119
File Structure

• Symbolic
• chmod ux,gw,or
• Numberic
• r 4
• w 2
• x 1
• rwx7
• rw-6

120
File Structure

• Links
• ln -- link command
• ln associate_file destination
• hard link
• soft link
• ls -i

121
File Structure

• Question
• ????
• BREAK

122
Redirection

• Standard Input
• Standard Output
• Redirect Output
• cat gt test
• cntl-d to end
• Redirect Input
• command arg lt filename

123
Redirection

• Appending
• Use command gtgt
• Examples

124
Pipes

• command_a arg command_b arg
• command_a gt temp
• command_b lt temp
• rm temp
• Examples

125
Filter

• Processes an input stream of data to produce an
  output stream of data
• who sort lp
• who tee test grep user

126
Metacharacters

• ?
• ,,,
• ...

127
UNIX/NFS Permissions

• NFS file permissions
• Read (r)
• Write (w)
• Execute (x)
• Permissions listed in sequence of
• User
• Group
• World (all other users on system)

128
File Permissions vs. Directory Permissions

• Permission File Directory
• Read r display/ list content copy
• Write w modify files add/delete
• Execute x execute control directory access

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Default Permissions

• Default permissions after creation

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The chmod Command

• Change permissions
• Syntax chmod opcode filename
• Example chmod uw test
• Gives you permission to write to file test
• Does not influence existing permissions
• Example chmod gr test
• Gives your group permission to read file test
• Does not influence existing permissions

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chmod Permission Categories

• u - user
• g - group
• o - others (world)
• a - all

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Taking Permissions Away

• chmod g-x
• Takes execute permission away from group
• Does not change r and w permissions

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Absolute Permissions

• chmod ox
• Assigns execute permission to others
• Example chmod ax test
• Sets permissions to execute ONLY
• r and w permissions are eliminated

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Setting Permissions Using Symbolic vs. Numeric
Mode

• Symbolic mode
• rwx rwx rwx
• Example chmod ur test
• Numeric mode
• 421 421 421
• Example chmod 700 text
• Possible to set absolute permissions only

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Redirecting Screen Output

• Prevent output from echoing to screen
• Is sent to file/printer instead
• Example ls gt test.out
• Sends ls listing to file test.out
• Caution Existing file will be overwritten
  without warning!
• Use gtgt option to append existing file
• Example ls gtgt test.out

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Capturing Keystrokes

• Record keystrokes
• Use cat command
• Syntax cat gt filename
• Type text to capture to file
• Press Ctrl-D to stop capturing and write to
  specified file
• Example cat gt test.out

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Piping

• Use the (pipe) character
• Modifies or redirects previous command in line
• Example man ls more
• Displays help for the ls command one screenful at
  a time
• Example who sort lp
• Sends a sorted list of currently logged-in users
  to the printer
• Note lp command must be last command

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Communicating in UNIX

• Real-time communication
• write
• talk
• E-mail communication
• mailx

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The write Command

• Send instant message to other user on UNIX system
• Similar to chatting
• Recipient must permit messaging
• Type mesg y at prompt
• Example write geisslm
• Opens write session with user geisslm
• End conversation with oo (over and out)
• Press Ctrl-C to end transmission

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The talk Command

• Similar to write command
• Divides user screen into two windows
• Statements displayed in opposite window on other
  end of communication

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The mailx Command

• Send electronic mail from UNIX system
• Syntax mailx username
• Type subject line
• Type message
• Press Ctrl-D to send message
• Example mailx geisslm
• Type subject line and message
• Example mailx geisslm lt message.fil
• Sends file message.fil to user geisslm

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Using mailx Interactively

• Many options available
• Type ? at ? prompt to view list of available
  options
• Example t 2
• Types second message on screen
• Example delete 3 (or d 3)
• Deletes message number 3 from message list
• Example h
• Displays list of message headers

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Mail Message Listing

• Message type
• N - new message
• R - read message
• O - old message
• Sender
• Date and time
• Size
• Subject

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Changing Message Options

• Possible to change options while typing message
  text
• Use (tilde) character options
• Be sure to specify option after issuing command
• Otherwise information may be missing
• Specify in mailx command line
• mailx -s E-mail test geisslm lt test.doc
• Sends file test.doc to user geisslm with subject
  E-mail test

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More About mailx

• Replying
• r replies to all recipients of original message
• R replies to sender of message ONLY

146
Exiting mailx Input Mode

• quit command processes messages
• exit command leaves mailbox untouched

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Aliasing

• Alias
• For one username
• For multiple usernames
• Distribution list
• Example alias entry in .mailrc file
• .mailrc is UNIX customization file
• Entry alias users user1 user2
• Mail sent to alias users is forwarded to user1
  and user2
• Create current-session alias at prompt

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Alias Advantages

• Issue multiple commands through one alias
• Example alias homeclearcdpwdls
• Clears the screen, changes to home directory,
  displays current directory and its contents
• Rename UNIX commands to DOS commands
• Example alias dirls -l
• Possible to issue DOS-like dir command to view
  contents of current directory

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Removing Aliases

• Use unalias command to remove alias(es)
• Example unalias test
• Removes test alias in current session

150
Thats All, Folks!

• Course Review
• Final Exam