Customizing the environment The different shells

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Customizing the environmentThe different shells

• Chapter 17 in Textbook

2
Which shell?

• User can choose his/her shell of preference
• sh (Bourne), ksh (Korn), bash (Bourne Again), csh
  (C-shell), tcsh (T shell) are options
• Commonly divided into Systems programming and
  Application programming shells

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Which shell? Differences

• Each shell has internal (built-in) and external
  command that might behave somewhat different
• Environment variables further modify the behavior
  of each shell
• Shell is your interface with the Kernel, so
  choose one that suits your style

4
Find the differences

• The chsh (change shell) command is available in
  some systems to change your default shell
• Not in apache.utdallas.edu.Contact your
  Administrator to change your default shell, but
  first test drive it
• ksh and csh will be covered here

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Systems vs. application

• sh (Bourne)
• ksh (Korn)

• csh (C)
• tcsh (T)

bash (Bourne again)
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Korn Shell (ksh)

• Created by David Korn under contract for ATT in
  1985.
• Incorporates the syntax of Bourne Shell for most
  portability (superset)
• Is the fastest for executing scripts (500 more
  than csh and up to 15000 more than Bourne)

7
ksh Features

• String functions similar to BASIC
• Variable typing (string, int, right-just, etc)
• Variable assignment (value when declared)
• Automatic menu creation function (select)
• Functions
• Arithmetic evals (increment and decrement)
• Command editing using vi(1) or emacs(1G)

8
Running/exiting ksh

• In order to run a ksh you type it in the command
  line
• ksh
• To return to your original shell
• exit

9
Variables

• Assigning a value
• VAR110
• VAR1VAR2
• Null value, useful for testing conditions
• VAR2
• To view the contents
• print VAR1
• 10
• Environment variable
• PATHPATH/usr/bin
• Note no spaces allowed around

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Exporting variables

• var110
• print var1
• 10
• ksh
• print var1
• exit
• export var1
• export var220
• ksh
• print var1 var2
• 10 20

null value
set and export in the same line
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set command

• View a list of local and environment variables
  values
• set
• PATH /usr/bin..
• var10
• Set and unset Korn shell attributes
• set -o lists attributes and their
  state (on/off)
• set -o option enables the option
• set o option disables the option

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set command

• To automatically export all new variables
• set -o allexport
• To disable the automatic export
• set o allexport

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History

• Keeps a list of executed commands
• Allows the re-execution of commands
• Allows modification prior to re-execution
• Keeps history between sessions in
• HOME/.sh_history

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History

• history
• 121 who
• 122 ls
• ...
• 136 pwd
• history -2
• 150 vi homework
• 151 cp homework homework.bak
• 152 history -2
• history 121 124
• ...
• history 144

Displays the last 16 by default
Displays the last n the history call
Displays a range
Displays from this number to the end
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History variables

• The size of the list is specified by
• HISTSIZE100
• An alternate history file can be specified
• HISTFILE.hist

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Re-executing commands

• Last command
• r
• Last command starting with a c
• r c
• Re-executing a command using a specific history
  number
• r 189

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Command line editing

• Fix and re-execute the last command
• ls myfle
• myfle no such file or directory
• r flfil
• ls myfile
• myfile
• Using the history number
• r libbin 211
• /usr/bin/X11/xcalc

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Setting vi to scroll through commands

• set VISUALvior set o vi
• Use or k
• to move backward
• Use or j to move forward
• Press enter to re-execute the command

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vi to edit commands

• 0 moves to the beginning of the line
• moves to the end of the line
• l moves the cursor to the right
• h moves the cursor to the left
• a appends after the cursor
• i inserts before the cursor

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Aliasing

• Set a new alias
• alias rmrm i
• Check for existing aliases
• alias
• Aliases can be configured in one of two files
• HOME/.profile
• HOME/ENV

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Aliasing

• Turn off aliasing for one occurrence
• \rm file
• Unset all aliases
• unalias a
• Unset a specific alias
• unalias rm

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Search order

• Alias
• Built-in command
• Functions
• Hash list
• PATH variable

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cd capabilites

• cd to previous directory
• cd -
• cd shorthand
• cd /home/lee/programs
• cd lee paty
• cd /home/paty/programs

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CDPATH variable

• export CDPATH .../
• pwd
• /home/paty
• cd bin
• /home/paty/bin
• cd etc
• /etc
• cd bin
• /bin

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Tilde ()

• cd current user is lee
• pwd
• /home/lee
• cd paty paty being a valid user
• pwd
• /home/paty
• cd /bin a directory under lees
  home
• pwd
• /home/lee/bin

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Filename expansion

• Set
• VISUALvi
• or
• set o vi
• Type the partial name and then use thesequence
  \
• For a list of options, use

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I/O redirection

• Input and output redirection is standard across
  shells
• ls l list
• ls l list
• sort

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Standard error

• Write the errors to a file
• find / -name test 2 error-file
• Write the errors to a terminal
• find / -name test 2 /dev/pts/130
• Throw away the errors
• find / -name test 2 /dev/null

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Standard output and standard error

• To different files
• find / -name test results 2 errors
• To the same file
• find / -name test results 21

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ksh configuration files

• /etc/default/login
• Configures basic settings for all users (path,
  umask)
• /etc/profile
• Configures basic settings for all ksh users
  (PATH, umask, mail)
• HOME/.profile
• Configures settings for each new ksh (set calls)
  if it exists. Analogous to .login in csh
• HOME/ENV
• Configures settings for Korn shell once at login
  (alias, history, prompt). Analogous to .cshrc

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C-Shell

• Developed by Bill Joy at U.C. Berkeley
• Same functionality and programming constructs of
  Bourne Shell, different keywords
• First shell focused on interactivity

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csh vs sh

• csh Added
• command aliasing
• command history
• command editing
• job control

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running C-Shell

• C-shell was created as the default user shell
  in some versions of Unix (now bash holds that
  title)
• In order to run a csh you type it in the command
  line
• csh

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csh local variables

• To set the value
• set prompthostname -s
• set noclobber
• set var1var2
• set path (path /usr/bin)

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csh local variables

• To list local variables
• set
• To unset a variable
• unset noclobber

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csh environment variables

• To set the value of an environment variable
• setenv DISPLAY 139.1.2.30.0
• List variables and their values
• env
• printenv
• Unset a variable
• unsetenv DISPLAY
• Note No equal sign is necessary (common error)

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csh predefined variables

• System-defined local variables
• Some need to be enabled, others need a value
• Enable filename completion
• set filec
• Store the last 50 commands
• set history50

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History

• csh history can be used to
• Re-execute previous commands with or without
  changes
• Reduce the amount of keystrokes
• To enable history we simply assign a value
• set history50

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History

• When we logout, history is lost
• To keep all or a portion of it
• set savehist50
• History is between sessions is kept in
• HOME/.history

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How to use history

• Can view portions of the list
• To view the last 3 commands
• history 3
• 96 ls
• 97 who
• 98 pwd

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Re-execute the last command
!!
!-2
Re-execute the second tothe last command
!97
Re-execute the command at entry 97 in the history
!cd
Re-execute the last commandstarting with cd
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Command line editing

• ls myfle
• myfle no such file or directory
• flfil
• ls myfile
• myfile

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Alias command

• An alias is an alternative name (usually shorter)
  to
• Create customized commands
• Execute multiple commands with fewer keystrokes
• Speed up commonly executed tasks

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Alias syntax

• Creating an alias Disabling alias once
• alias rm rm i \rm
• Displaying existing aliases
• alias
• rm (rm i)
• Eliminating a specific alias
• unalias rm
• Eliminating all aliases
• unalias

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Search order

• Aliases
• Built-in commands
• Hash list (list of previous path searches)
• Path

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Using History with alias

• History events fields are separated by white
  space
• 98 cp r project1/status /usr/martha/status
• You can use this field numbering scheme to create
  an alias with user arguments.
• alias loc find \!2 name \!1

0 1 2
3
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The special character

• An abbreviation of a users home directory
• It is used in one of two ways
• Change to joes home directory
• cd joe
• Change to the home directory of the account used
  for login
• cd

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Filename Completion

• To enable filename completion
• set filec
• Filename completion allows the C shell to
  complete the name of a file or directory
• Use the ESC key for name completion
• Attempts to match the unique character pattern
  provided by the user
• Use Ctrl-D when signals a non-unique
  pattern.

49
C-shell Special characters

• works as an abbreviation
• chmod ugo-w proj1,12/goals
• Instead of
• chmod ugo-w proj1/goals proj12/goals

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Redirecting Standard Input and Output

• Standard across shells
• mail bob
• cat file1 file2 file3 files
• cat file4 files

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clobbering

• Redirecting the output to an existing file
  destroys (clobbers) the contents of the file
• Use to append information
• Set the noclobber local variable to prevent
  accidental clobbering
• set noclobber
• cat memo1 memo2 memo3 files
• Files File exists
• Use the ! Symbol override noclobber
• cat header file1 ! files

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Redirecting Standard Error

• Send both output and errors to the same file
• find / -name letter /find.out
• Send standard output and errors to different
  files
• (find / -name letter /find.out) find.errs

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Redirecting Standard Error

• Send the output to the terminal screen (window),
  and errors to /dev/null
• (ls -R /dev/tty) /dev/null
• Send the output to find.out and errors to the
  "bit bucket"
• (find / -name letter /find.out) /dev/null

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C Shell Configuration Files

• /etc/default/login
• Configures basic settings for all users (path,
  umask)
• /etc/cshrc
• Configures basic settings for all C shell users
  (motd, mail)
• HOME/.cshrc
• Configures settings for each new C shell (alias,
  history, prompt)
• HOME/.login
• Configures settings for C-shell once at login
  (environment variables, i.e DISPLAY)