Introduction to Unix

1
Introduction to Unix

• Class Room 336
• Instructor Anthony Richards

2
The C Shell

• A command interpreter
• A high-level programming language

3
Accessing Shells

• csh for C Shell
• sh for Bourne Shell
• jsh for Job Shell
• ksh for Korn Shell
• ps to display process status and shell

4
Some C Shell Features

• History - Keeps a list of recent commands
• Alias - Allows renaming of commands
• Job control - move jobs to background or
  foreground
• Directory Stack - keeps a list of dirctories
  and allows easy movement between them

5
History

• history displays a list of recent commands
• set history n instructs the shell to save the
  number of events specified by n.
• set savehist n directs the shell to make the
  number of commans specified by n available across
  sessions.

6
Reexecuting Events

• !n reexecutes the event specified by n
• !! reexecutes the previous event
• ! -5 executes the fith preceeding event

7
Modifying Previous Events
Space

• place a and an a modifier after an event number
  in order to modify it.
• !!s/car/cat will replace car with cat in the
  most recent event and execute it.
• can be used to referr to the most recent event.
• carcat also replaces car with cat in the most
  recent event.
• page 349 event modifiers.

8
Aliases

• provide short hand names for commands.
• alias short hand actual command
• allias ll ls -l will execute ls -l when ll is
  entered.
• alias with no arguments will display a list of
  aliases.
• unalias removes an alias.
• alias alias name displays the command for the
  alias.

9
Job Control

• runs a job or command in the background.
• fg n moves the job specified by n from the
  background to the foreground.
• To place a running job in the background
  stop the job
  with either stop of CTRL Z then type bg

10
Redirecting Standard Error

• gt file name will redirect the standard error
  to the file specified by file name.

11
Filename Generation

• The C Shell uses to generate filenames.
• by itself expands to your home directory
• username reffers to the home directory of the
  user specified in username.
• cp letter.txt caax000 copies letter.txt tothe
  home directory of user caax000.

12
Filename Completion

• command part of filename ESC will cause the
  shell to complete the file name.

13
Directory Stack

• The directory stack is a list of directories in
  use.
• The directories can be accessed and manipulated
  with teh pushd and popd commands.
• dirs displays the list of directories in use. It
  displays working directory if the stack is empty.

14
pushd

• pushd (push directory) provides an easy way to
  navigate between directories.
• pushd directory changes to directory and places
  it at the top of the stack.
• pushd with no arguments makes the second
  directory in on the stack the working directory
  and places that directory at top of stack.

15
Stack Numbers

• Directories on the stack are numbered from 0,
  the top directory to nn, the total number of
  directories.
• pushd n will move to the directory specified by
  n and place it at the top of the stack
• popd (pop irectory) removes a directory from the
  stack

16
popd continued

• popd removes the directory at the top of the
  stack.
• popd n removes the directory specified by n from
  the stack.

17
Variables

• variable names can be up to 20 characters in
  length.
• They can consist of letters digits and
  Underscores.
• The first character cannot be a digit.

18
Variable Types

• String Numeric calculations cannot be performed
  on them
• Numeric Numeric calculations can be performed on
  them.

19
Variable Declaration and Assignment

• set variable name value declares a string
  variable and assigns the value to it.
• set name sue spaces are allowed betwen the
  in the c shell
• set variable name initializes the variable to a
  null string
• set name
• unset variable name removes the variable name
  from the declared variable list.

20
Variable Declaration Continued

• set with no arguments displays the list of
  declared variables and their values.

21
Arrays of String Variables

• set array variable name ( array element values
  ) declares a string array variable and assigns
  values to its elements.
• set colors (red green blue orange yellow)
• array variable namen references the nth element
  of array variable name
• echo colors5
• set colors3 purple
• echo colors2-4

22
Numeric Variables

• _at_ variable name operator expression declares a
  numeric variable and assigns a value to it.
• The assigned value must be numeric.

23
Sample Numeric Assignments

• _at_ count 0 assigns 0 to count
• _at_ count ( 5 2) count is 7
• _at_ result ( count lt 5) returns 0 because count
  is gt 5
• _at_ count 5 adds 5 to count
• _at_ count adds 1 to count
• _at_count-- subtracts 1 from count

24
Numeric Arrays.

• must be declared with set before values can be
  assigned.
• values can be assigned to entire array or to
  single elements.
• The index must be a numeric constant or a numeric
  variable. It cannot be an expression.

25
Sample Numeric Array Declaration

• set ages (0 0 0 0 0) declares an array called
  ages with five elements.
• _at_ ages2 15 assigns 15 to second element
• _at_ ages3 (ages2 4)

26
Braces

• use braces to separate a variable from other text
  without using spaces.
• set prefix Alex
• echo prefix is short for prefixander

27
Special Forms of User Variables

• variable name gives the number of elements
  in an array
• ?variable name returns 1 if the variable has
  been declared and 0 if it has not been declared

28
Lab 6Due November 24

• page 380 1-7