TDC368 UNIX and Network Programming Camelia Zlatea, PhD Week 9:  Introduction to UNIX Shells  C-Shell Interactive Commands  C Shell Programming

UNIX Network Programming – TDC Page 2 Spring 2003 References  Ellie Quingley, UNIX Shells by Example, Prentice Hall PTR, NJ, 1997 chap.9 (pp )  Dave Curry, UNIX Systems Programming for SVR4, O'Reilly & Assoc., Sebastopol, CA,  UNIX in a Nutshell, by Daniel Gilly, O’Reilly & Associates, Inc., section 5.

UNIX Network Programming – TDC Page 3 Spring 2003 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 (pid=1), 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

UNIX Network Programming – TDC Page 4 Spring 2003 Introduction to UNIX Shells  ? How to change your login shell: passwd –e (on HP)  File.cshrc contains C shell variables settings  Example: set history=20 # previous commands to remember. set savehist=20 # number to save across sessions. set system=`hostname` # name of this system. set prompt = "$system\:> " # command prompt. set autologout=20 alias l ls alias info ‘(who am i; date )’

UNIX Network Programming – TDC Page 5 Spring 2003 Introduction to UNIX Shells  File.login contains environment variables and terminal settings; this information is inherited by shell’s 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

UNIX Network Programming – TDC Page 6 Spring 2003 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 >csh.doc &  Command line history: history –!! # re-executing last command –!6 # the sixth command from history is executed

UNIX Network Programming – TDC Page 7 Spring 2003 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-Z][A-Z][A-Z] #list all files with three uppercase character name ls *{11,22} #list all files ending in 11 or 22

UNIX Network Programming – TDC Page 8 Spring 2003 C-Shell Interactive Commands  Redirectation, Pipes –( >, &, >>, >>&, << HERE, |, |&  Example: Here Document cat << 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

UNIX Network Programming – TDC Page 9 Spring 2003 C-Shell Interactive Commands  Redirectation of both output and error standard files >& –ls -l | grep May > & outfile –separate redirectation of stderr and stdin –( ls -l | grep May > result1 ) > & 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.

UNIX Network Programming – TDC Page 10 Spring 2003 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 $machine # echo the value of variable machine, if it is defined set var = noon # user variable echo after${var} 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

UNIX Network Programming – TDC Page 11 Spring 2003 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 $persons[$#persons] # display the last element echo $persons[1] #display first element of the array set $persons[1] = John #reassign first element echo $persons[3-4] # list elements 3 and 4 of the array echo $persons[10] # out of range shift persons # shift one position to the left the array values set days = "Monday Tuesday Wednesday" #a string variable, not an array set days = ($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

UNIX Network Programming – TDC Page 12 Spring 2003 Special variables  $$ - displays the PID of current shell  $< - accepts input from the user  Backslash Character: - escape the interpretation of a single character (ex. ?, !, newline)

UNIX Network Programming – TDC Page 13 Spring 2003 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 $SHELL echo "This machine is `uname –n`" echo The calendar for this month is cal echo The processes you are running are: ps -al | grep "^ *$LOGNAME" echo "Thanks for coming. See you soon\!\!" echo Good-bye $LOGNAME

UNIX Network Programming – TDC Page 14 Spring 2003 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

UNIX Network Programming – TDC Page 15 Spring 2003 Variables  set varname = # assignment $< variable # reading user input  Numeric Variables - Arithmetic Expressions Operators: + - / * > (right shift) +=, -+, *=, /=, ++, --  var = 5+ 3 echo sum += 1 # same sum sum +1 echo $sum

UNIX Network Programming – TDC Page 16 Spring 2003 Command Line Arguments  $0, $1,.., $9, ${10}, ${11},.. $* - all arguments $argv[1], $argv[2], …. – 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 = $d[1-3] echo Welcome to this day $dd echo Hope you have a nice day, $argv[1] \! echo Good-bye $argv[1] $argv[2] $argv[3] greetings Joe Doe

UNIX Network Programming – TDC Page 17 Spring 2003 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

UNIX Network Programming – TDC Page 18 Spring 2003 Example #!/bin/csh -f # Scriptname: filecheck # Usage: filecheck filename set file=$1 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

UNIX Network Programming – TDC Page 19 Spring 2003 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

UNIX Network Programming – TDC Page 20 Spring 2003 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 condor:> csh t2 a b c d e a b c d e b c d e c d e d e e condor:>

UNIX Network Programming – TDC Page 21 Spring 2003 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 echo "Out of all loops"

UNIX Network Programming – TDC Page 22 Spring 2003 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

UNIX Network Programming – TDC Page 23 Spring 2003 Setting Executable Scripts  setuid scripts  chmod u+sx script_file

UNIX Network Programming – TDC Page 24 Spring 2003 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 = $< # read input variable if ($fname =~ [Ss][Tt][Oo][Pp]*) then break # exit if stop is typed endif echo "Last Name (XX to restart) " set lname = $< if ($lname =~ "XX")then goto startover # skip rest of the loop endif echo "$fname $lname's phone number (XX to restart): " set phnbr = $< if ($phnbr =~ "XX")then goto startover # skip rest of the loop endif

UNIX Network Programming – TDC Page 25 Spring 2003 A C shell script to add new data entries to a phone list file2/3 # 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 = $< if ($answer =~ [Yy]*) then goto startover else break endif end endif

UNIX Network Programming – TDC Page 26 Spring 2003 A C shell script to add new data entries to a phone list file3/3 # insert entry set correct=n while ("$correct" !~ [Yy]*) echo "1 $fname“ ; echo "2 $lname“ ; echo "3 $phnbr“ ; echo "Is this correct ? (y/n)" set answer=$< if ("$answer" =~ [Yy]*) then set correct=y else echo "Number to correct: " set num = $< switch ($num) case 1: echo "Last Name: " set fname = $< breaksw case 2: echo "Last Name: " set lname = $< breaksw case 3: echo "Phone Number: " set phnbr = $< breaksw endsw endif end # end while... correct echo "$lname, $fname $phnbr" >> $phonefile end # first while echo "Done"

UNIX Network Programming – TDC Page 27 Spring 2003 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"

UNIX Network Programming – TDC Page 28 Spring 2003 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: $0 pattern echo "pattern is what to look for in the phone list" breaksw default:set counter=0 foreach pattern ($*) if {(grep "$pattern" $phonefile)} counter++ else echo "$pattern not found in $phonefile" endif end breaksw endsw echo "Matched $counter patterns" echo "Done"

UNIX Network Programming – TDC Page 29 Spring 2003 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 > /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"