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TDC368 UNIX and Network Programming

TDC368 UNIX and Network Programming. Week 9: Introduction to UNIX Shells C-Shell Interactive Commands C Shell Programming. Camelia Zlatea, PhD Email: czlatea@cs.depaul.edu. Ellie Quingley, UNIX Shells by Example, Prentice Hall PTR, NJ, 1997 chap.9 (pp.317-414)

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TDC368 UNIX and Network Programming

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  1. TDC368UNIX and Network Programming Week 9: • Introduction to UNIX Shells • C-Shell Interactive Commands • C Shell Programming Camelia Zlatea, PhD Email: czlatea@cs.depaul.edu

  2. 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, O’Reilly & Associates, Inc. , section 5. References

  3. 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

  4. 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 )’

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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.

  10. 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

  11. 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

  12. Special variables • $$ - displays the PID of current shell • $< - accepts input from the user • Backslash Character: - escape the interpretation of a single character (ex. ?, !, newline)

  13. 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

  14. 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

  15. Variables • set varname = # assignment $< variable # reading user input • Numeric Variables - Arithmetic Expressions Operators: + - / * <<(left shift) >> (right shift) +=, -+, *=, /= , ++, -- • Examples: @ var = 5+ 3 echo $var @ sum += 1 # same with @ sum = @ sum +1 echo $sum

  16. 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

  17. 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

  18. 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 endif

  19. 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

  20. 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:>

  21. 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"

  22. 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

  23. Setting Executable Scripts • setuid scripts • chmod u+sx script_file

  24. 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

  25. 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 = $< if ($answer =~ [Yy]*) then goto startover else break endif end endif

  26. A C shell script to add new data entries to a phone list file 3/3 # 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"

  27. 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"

  28. 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" $phonefile)} then @ counter++ else echo "$pattern not found in $phonefile" endif end breaksw endsw echo "Matched $counter patterns" echo "Done"

  29. 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"

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