CIS52 Week 2

1
CIS52 - Week 2

• Printing (ATT versus BSD)
• Introduction to the Bourne Shell

2
Class 1 Review

• For anyone wearing blue
• Name the three most common shells
• What command is used to get help in unix
• Who were the primary authors of Unix
• What two organizations were most influential in
  the development of Unix
• How do you get a listing of your home directory

3
Class 1 Review

• For anyone in rows one or two
• pwd
• cd
• cat
• dog
• tail
• wc

4
Class 1 Review

• What are the three modes in vi
• Name four ways to get into input mode
• While in command mode, how do you move your
  cursor one character to the left
• How do you save your work in vi
• How do you delete a line
• How do you go to the fourth line

5
Printing (ATT variety)

• Typical command is lp
• Typical syntax lp myfile
• lp -o nobanner myfile
• Unix returns with acknowledgement
• request id is okidata-3 (if that is the printer
  name)
• Cancel your print job
• cancel okidata-3

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Printing Continued

• To get status
• lpstat
• To get the mail system to alert you when printing
  has completed
• lp -m
• Printing on YOUR version of Standard Unix is
  guaranteed to be different

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Printing BSD vs ATT

• BSD (also LINUX)
• lpr
• lpq -Pokidata n01
• lpr-Pokidata -5 file
• lpq -Pokidata
• lprm -Pokidata-1
• lpr -Plaser myfile

• ATT
• lp
• lpstat
• lp -n5 file
• lpstat -t
• cancel okidata-1
• lp -dlaser myfile

8
Time for Some Feedback

• Does lp trace its roots to UC Berkeley?
• NO .. lp indicates ATT
• How do you get the status of a job ?
• lpstat in ATT
• lpq in BSD
• How do you cancel a job using ATT ?
• cancel request

9
Printing for the printer-less

• How do you print using the SCC LAB facility?
• Use Telnet logging feature to record data going
  to screen to a file on local machine
• OR
• use FTP to grab file from server, print in w95
  (using notepad)

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This question is for anyone wearing red

• Do you remember the command option (using ATT
  syntax) for skipping the printing of a banner?
• What are the pros and cons of teaching users to
  use this option?

11
And now .. On to the SHELL!

• Some Background
• The Command Line Syntax
• How the tty driver gets involved
• Special characters
• Streams and Redirection
• Pipes and Filters
• Feedback

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Some Background

• The Shell provides an interface for
• controlling programs
• handling input and output
• The Bourne, Korn and C shells
• ARE LINE ORIENTED
• DATE BACK TO THE USE OF THE TELETYPE

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The Command Line Syntax

• Command option_arguments other_arguments
• most commands accept one or more arguments
• An argument is a filename, string of text or some
  other object
• some, like ls do not require any
• an option argument usually starts with a dash (-)
  and modifies the command somehow

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Command Examples

• ls
• ls -l
• cat myfile1 myfile2 myfile3
• sort -r myfile
• grep aardvark myfile
• grep -v aardvark myfile

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More fascinating facts about Commands

• Command lines must be no greater than 512
  characters (on my version of unix)
• more than one command can be put on a line if you
  separate them with a colon
• ls cat myfile
• commands can be grouped with ( )
• cd (cd /mysubdir pwd ls -a) pwd
• cd within () only affects commands in ()

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How the tty driver gets involved

• The tty driver manages communication between UNIX
  and the terminal
• It buffers lines until you type a return key
• After a return key is typed, it passes the
  complete line to the shell
• The tty driver responds to special characters
  (backspace, U, r or R)

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Telnet and special characters

• Issue the stty-a command
• presents special key sequences that let you kill
  a process (\ C for example)
• Our WIN95 Telnet seems to capture these key
  strokes, so they are not passed to the UNIX
  server
• Log into the server from another terminal to kill
  a process

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Method to kill a process

• Login to UNIX on another terminal
• Issue the ps command
• Write down lowest process id number
• (this was for your prior runaway session)
• Issue kill -9 xxxx
• where xxxx is the number

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Special characters

• The SHELL has first grabs on input sent from a
  terminal via the tty driver.
• It may, in looking at the stream of characters,
  decide that one of them is special
• Some of these special characters are used for
  filename expansion, paths,redirection,
  sequencing, etc

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Filename Expansion

• Asterisk () wildcard for all characters, except
  those that start with a period
• cat cis52 or ls .c
• Question Mark (?) wildcard for a single
  character
• ls assignment?
• Character Class
• ls assignment123

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Formal Definition

• Filename expansion refers to the process of
  expanding ambiguous file references
• also referred as globbing
• (but only by Unix nurds who want you to think
  they are wonderful)

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Other Special Characters

• for command sequencing (separation on the same
  line)
• used to run process in the background (which
  lets you keep working at the terminal)
• / part of a pathname
• cat /class/n01/myfile
• comment (in shell script)

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Streams and Redirection

• Stream a sequenced source of bytes
• keyboard is input stream
• screen is output stream
• a file can be used with either
• input if read
• output if write
• Tapes and Disks can be used with input or output
  streams

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(No Transcript)
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Unix Streams

• All programs are connected to 3 Streams
• 0 Standard Input (kb is default)
• 1 Standard output (screen is default)
• 2 Standard Error (screen is default)
• Redirection refers to a way in which you can get
  the shell to alter these defaults

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Redirection

• Command filename
• takes output from a command and sends it to a
  file
• command filename
• takes output from a command and appends it to
  a file
• command
• takes input from a file and sends it to the
  command

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Redirection Continued

• command 1 filename is what is really happening
  when you type
• command filename
• command 2 filename sends standard error to a
  file

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Examples

• wc file1
• wc file1 file2
• wc file2
• wc file1 file2
• wc file 2
• start typing one or more lines
• d

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Examples

• cat apple orange
• cat apple orange apple
• cat homework? temp
• cat ?ome temp

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Filters

• A filter is a command that expects input directly
  from the standard input and sends output to the
  standard output
• ls is not one .. It does not read data from
  standard in or a file.
• wc however, is a filter (as are many of the
  commands we will talk about)

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Filters continued

• A filter
• reads input stream
• transforms the data
• writes an output stream
• can read/write to any file or device

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Pipes

• A pipe is similar to redirecting the output of a
  command to a file, except that it redirects it to
  ANOTHER COMMAND
• The vertical bar is used to designate a pipe
  
• The Shell establishes the connection
• Data in the pipe may be buffered in memory

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Examples

• who wc -l
• ps wc -l
• cat wordlist tr a A
• who tee temp
• who sort temp

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Feedback

• rm
• ls -l new
• more chap135
• rm .o
• ls ???
• ls a-z
• ls a

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Metacharacter suppression

• Metacharacter is computer nurdese for the word
  special
• Single quotes
• suppress the special meaning of all special
  characters (Keeps the shell from interpreting
  them)
• Double Quotes
• suppress all except \, and

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Examples

• cat homework
• cat myvar
• cat myvar
• cat /class/n01/myfile
• cat /class/n01/myfile

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Command Substitution

• One more metacharacter that the shell interprets
• the backquote () used in pairs
• tells the shell to treat the letters between the
  backquotes as a command and to execute it first
• example
• wc ls

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Bonus UNIX HUMOR

• From the UNIX HATERS GUIDE
• Two of the most famous products of Berkeley are
  LSD and UNIX. I dont think that is a coincidence
• Unix Programmers have a criminally lax attitude
  toward error reporting and checking

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Comment on Unix mail program

• Im rather surprised that the author of sendmail
  is still walking around alive
• One of the recommended books for learning
  sendmail (Costales, et al from OReilly) has a
  bat on the cover. There are several reasons why
  people think this is appropriate

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Why does the Costales book have a bat on the cover

• Both bats and sendmail are held in low esteem
  by the general public
• bats require magical rituals involving crosses
  and garlic to get them to do what you want to do.
  So does sendmail

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UNIX ERROR MESSAGES

• rm clinton-ethics
• rm clinton-ethics non existent
• How would you match Dan Quayles incompetence
• unmatched
• man why did you get a divorce
• man too many arguments

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Unix Error Messages

• What is saccharine?
• Bad substitute
• drink
• bottle cannot open
• opener not found
• got a light?
• No match

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Unix Error Messages

• (where is jimmy hoffa
• Missing )
• touch me
• chmod 000 me
• touch me
• touch cannot touch me permission denied