TDC368 UNIX and Network Programming

1
TDC368UNIX and Network Programming

• Week 9
• Introduction to UNIX Shells
• C-Shell Interactive Commands
• C Shell Programming

• Camelia Zlatea, PhD
• Email czlatea_at_cs.depaul.edu

2
References

• Ellie Quingley, UNIX Shells by Example, Prentice
  Hall PTR, NJ, 1997 chap.9 (pp.317-414)
• Dave Curry, UNIX Systems Programming for SVR4,
  O'Reilly Assoc., Sebastopol, CA, 1996.
• UNIX in a Nutshell , by Daniel Gilly, OReilly
  Associates, Inc. , section 5.

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Introduction to UNIX Shells

• shell the program interface between the user
  and the kernel functions
• reading user input and parse the command line
• managing processes and jobs redirection, pipes
• handling signals
• executing scripts
• System Startup
• process init (pid1), the first process to run
  after the system boots will fork and exec a
  program that handle terminals (getty).
• getty activates the terminal port stdin, stdout
  and stderr.
• same process executes next the command
  "/bin/login" prompts for user name and password
  validate the input by reading the correspondent
  entry from /etc/passwd setup working environment
  
• executes user predefined shell (ex. "/bin/csh")
• Environment Initialization (C Shell)
• C shell executes the file .cshrc (this is
  executed anytime when a new C shell is started)
• C shell executes .login file
• C shell prompt is displayed as a fact that shell
  is waiting to process user command

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Introduction to UNIX Shells

• ? How to change your login shell passwd e (on
  HP)
• File .cshrc contains C shell variables settings
• Example
• set history20 previous commands to
  remember.
• set savehist20 number to save across
  sessions.
• set systemhostname name of this
  system.
• set prompt "system\gt " command prompt.
  
• set autologout20
• alias l ls
• alias info (who am i date )

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Introduction to UNIX Shells

• File .login contains environment variables and
  terminal settings this information is inherited
  by shells children processes.
• Example
• setenv TERM ansi
• umask 077
• echo Hello LOGNAME
• echo The date is 'date'
• echo Your home shell is SHELL
• echo Good-bye LOGNAME
•  
• ? How to re-execute a modified .chsrc or .login ,
  in the current shell
• source .login or source .cshrc

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C-Shell Interactive Commands

• Command Line
• C shell status variable returns is set to the
  exit status (0 to 255) of the last executed
  command (0 success)
• Sequential execution of commands ()
• Example who am i pwd date
• Conditional Execution ( )
• Example grep czlatea /etc/passwd talk
  czlatea
• if command grep is successful (status 0) then
  mail command is executed
• Example grep tdc368 /etc/passwd echo "user
  tdc368 unknown"
• Pipelined Execution ()
• ls l sort
• Background Execution ()
• man csh cat gtcsh.doc
• Command line history history
• !! re-executing last command
• !6 the sixth command from history is executed

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C-Shell Interactive Commands

• Command Line Arguments
• !1 first , !2 second , !3 third ..
• ! - last , ! - first , ! - all arguments
• Example
• echo a b c d
• !0 ! re-execute the last command (echo)
  with only its last argument
• Job Control
• jobs
• Bg
• fg
• suspend jobs (Z)
• Metacharacters
• ls a list all files starting wirh a
• ls aA list all files starting with a or A
• ls 0-9 list all file ending with a digit
• ls .0-9 list allfiles ending with a
  period followed by a digit
• ls ?? list all files with two-character name
• ls A-ZA-ZA-Z list all files with three
  uppercase character name
• ls 11,22 list all files ending in 11 or 22

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C-Shell Interactive Commands

• Redirectation , Pipes
• ( gt , lt , gt, gtgt, gtgt , ltlt HERE, ,
• Example Here Document
• cat ltlt HERE
• This is a test for input re-directation.
• This show a here document.
• HERE
• the output of command cat is the "here document"
  from first HERE to second HERE

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C-Shell Interactive Commands

• Redirectation of both output and error standard
  files gt
• ls -l grep May gt outfile
• separate redirectation of stderr and stdin
• ( ls -l grep May gt result1 ) gt error
• C shell process forks a child to execute the
  above command
• The child process redirects its stderr and stdout
  to file errors
• The child process forks a new process
• The new process executes the command file in ( ..
  ) it inherits the file descriptors of its
  father it redirects again its stdout to file
  results.

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Variables in C Shell

• Local variables visible in the shell were was
  defined
• Environment variables visible in the shell and
  all processes spawned by this shell
• Example
• set history 50 set the build-in variables
• set savehist 10 history and savehist
• set person Doe set user variable username
• set machine uname n and machine
• echo ?machine test to see if variable machine
  is defined (set)
• echo machine echo the value of variable
  machine, if it is defined
• set var noon user variable
• echo aftervar
• set var "Hello World"
• echo var
• setenv PERSON"Joe Doe" set an environment
  variable
• echo PERSON
• set displays all local variables set for the
  current shell
• env display all environment variables
• setenv

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Arrays and Strings

• Examples
• set persons (Joe Liz Tom Dan) an array
  variable
• echo persons display the variable
• echo persons same
• echo persons display the number of elements
• echo personspersons display the last
  element
• echo persons1 display first element of the
  array
• set persons1 John reassign first element
• echo persons3-4 list elements 3 and 4 of
  the array
• echo persons10 out of range
• shift persons shift one position to the left
  the array values
• set days "Monday Tuesday Wednesday" a string
  variable, not an array
• set days (days) converts the string into an
  array
• set var1 date the output of the command
  date is stored as an array
• set var2 date" the output is stored as a
  single string

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Special variables

• - displays the PID of current shell
• lt - accepts input from the user
• Backslash Character - escape the interpretation
  of a single character (ex. ?, !, newline)

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C-Shell Programming

• Shell Scripts
• The magic number - !/bin/csh first line of the
  script
• Examples
• !/bin/csh
• echo Hello LOGNAME
• echo The date is date
• echo Your home shell is SHELL
• echo "This machine is uname n"
• echo The calendar for this month is
• cal 5 2003
• echo The processes you are running are
• ps -al grep " LOGNAME"
• echo "Thanks for coming. See you soon\!\!"
• echo Good-bye LOGNAME

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Debugging scripts set/unset echo

• set/unset verbose
• !/bin/csh
• echo Hello LOGNAME
• echo The date is date
• set verbose
• echo Your home shell is SHELL
• unset verbose
• echo Good-bye LOGNAME

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Variables

• set varname assignment
• lt variable reading user input
• Numeric Variables - Arithmetic Expressions
• Operators - / ltlt(left shift) gtgt (right
  shift)
• , -, , / , , --
• Examples
• _at_ var 5 3
• echo var
• _at_ sum 1 same with _at_ sum _at_ sum 1
• echo sum

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Command Line Arguments

• 0, 1, .., 9 , 10, 11, ..
• - all arguments
• argv1, argv2, . first, second arg. ..
• argv number of arguments
• argv all arguments
• Example
• !/bin/csh -f
• The greetings script
• This script greets a user whose name is typed
  in at the command line.
• echo 0 to you 1 2 3
• set d date
• set dd d1-3
• echo Welcome to this day dd
• echo Hope you have a nice day, argv1 \!
• echo Good-bye argv1 argv2 argv3
• greetings Joe Doe

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Decisions

• if , if-else, switch
• Examples Conditions and File testing
• !/bin/csh -f
• Script name logical
• set x 1
• set y 2
• set z 3
• if (( "x" "y" ) ! "z" ) then grouping
• echo TRUE
• else
• echo FALSE
• endif

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Example

• !/bin/csh -f
• Scriptname filecheck
• Usage filecheck filename
• set file1
• if ( ! -e file ) then
• echo "file does not exist"
• exit 1
• endif
• if ( -d file ) then
• echo "file is a directory"
• else if ( -f file ) then
• if ( -r file -x file ) then nested if
  construct
• echo "You have read and execute permission on
  file file.
• endif
• else
• print "file is neither a plain file nor a
  directory. "
• endif
• endif

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Example system type Testing

• !/bin/csh -f
  
• Program to determine the type of system you are
  on.
• echo "Your system type is "
  
• set release uname -n echo release
  
• switch ( uname -s)
  
• case SunOS
  
• echo SunOs
  
• breaksw
  
• case HP-UX
  
• echo HP
  
• breaksw
  
• case Linux
  
• echo Linux
  
• breaksw
  
• endsw

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Loops

• foreach variable (list)
• commands
• end
• Example
• !/bin/csh -f
• foreach file (.o)
• rm file
• end
• while (condition)
• Command
• end
• Example
• !/bin/csh -f
• Script is called loop.args
• while ( argv )
• echo argv
• shift
• end

condorgt csh t2 a b c d e a b c d e
b c d e c d e
d e e
condorgt
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Loop

• repeat n commands
• !/bin/csh -f
• while ( argv )
• echo argv
• shift
• end
• !/bin/csh -f
• while (1)
• echo "Hello, in 1st loop"
• while (1)
• echo "In 2nd loop"
• while (1)
• echo "In 3rd loop"
• repeat 3 break
• end
• end
• end
• echo "Out of all loops"

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Signals Handling

• An INT signal (ctrl-C) can be caught only from
  with a script
• !/bin/csh
• onintr done install signal handler label
  done
• sleep 30 other scripts commands
• echo Bye noINT
• exit
• done signal handler
• echo hello int
• onintr - disable interupts
• ls -l
• echo Bye

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Setting Executable Scripts

• setuid scripts
• chmod usx script_file

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A C shell script to add new data entries to a
phone list file 1/3

• !/bin/csh -f
• set phonefile phone.list
• startover
• while (1)
• echo "First Name (stop to exit) "
• set fname lt
  read input variable
• if (fname SsTtOoPp) then
• break exit if
  stop is typed
• endif
• echo "Last Name (XX to restart) "
• set lname lt
• if (lname "XX")then
• goto startover skip rest of
  the loop
• endif
• echo "fname lname's phone number (XX to
  restart) "
• set phnbr lt

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A C shell script to add new data entries to a
phone list file 2/3

• search for a duplicate entry
• if (egrep "lname, fname phnbr"
  phonefile) then
• echo "Duplicates were found in
  the list "
• endif
• while (1)
• echo "Cancel this entry?
  (y/n) "
• set answer lt
• if (answer Yy)
  then
• goto startover
• else break
• endif
• end
• endif

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A C shell script to add new data entries to a
phone list file 3/3

• insert entry
• set correctn
• while ("correct" ! Yy)
• echo "1 fname echo "2 lname
  echo "3 phnbr echo "Is this correct ?
  (y/n)"
• set answerlt
• if ("answer" Yy) then
• set correcty
• else
• echo "Number to correct
  "
• set num lt
• switch
  (num)
• 
  case 1 echo "Last Name "
• 
  set fname lt
• 
  breaksw
• 
  case 2 echo "Last Name "
• 
  set lname lt
• 
  breaksw
• 
  case 3 echo "Phone Number "
• 
  set phnbr lt

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A C shell script to find a pattern in a phone
list file

• !/bin/csh -f
• set phonefile phone.list
• switch (argv)
• case 0
• echo "Usage 0 pattern
• echo "pattern is what to look for in the phone
  list"
• breaksw
• default foreach pattern ()
• echo pattern
• grep "pattern" phonefile echo
  "pattern not found in phonefile
• end
• breaksw
• endsw
• echo "Done"

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A C shell script to find a multiple pattern in a
phone list file

• !/bin/csh -f
• set phonefile phone.list
• switch (argv )
• case 0 echo "Usage 0 pattern
• echo "pattern is what to look for in the phone
  list"
• breaksw
• default set counter0
• foreach pattern ()
• if (grep "pattern" phonefile) then
• _at_ counter
• else
• echo "pattern not found in phonefile"
• endif
• end
• breaksw
• endsw

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Example

• !/bin/csh -f
• A C shell script to take two arguments and
  substitute the second argument
• for the first, writing the resulting
  corrections back into the phone list file
• set phonefile phone.list
• switch (argv)
• case 2
• sed "s/1/2/g" phonefile gt
  /tmp/chg.tmp
• mv /tmp/chg.tmp phonefile
• breaksw
• default
• echo "Usage 0 old new
• echo "0 substitutes old for new in the
  phonelist"
• breaksw
• endsw
• echo "Done"