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Introduction to UNIX (3)

Introduction to UNIX (3). C Shells Start-up Variables Alias Script control structure. Start-Up. When a C shell is invoked, first execute commands in $HOME/.cshrc if it exists If the C shell is a login shell,

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Introduction to UNIX (3)

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  1. Introduction to UNIX (3) • C Shells • Start-up • Variables • Alias • Script control structure

  2. Start-Up • When a C shell is invoked, first execute commands in $HOME/.cshrc if it exists • If the C shell is a login shell, • Execute commands in global login initialization file (e.g., /.login) if it exists • Execute commands in $HOME/.login if it exists • Then it displays its prompt and wait for user commands

  3. .login File • Typically contains commands that set environment vars like $TERM or $PATH • Those that needs to be set once (that are inherited by other shells) or terminal setting set term = vt100 set path = ( . /usr/bin /usr/local/bin ) stty erase “^?” kill “^U” intr “^C” eof “^D” set history = 40 set prompt = “! % “

  4. .cshrc File • Typically contains commands that set common aliases or anything that applies to the current shell alias emacs /usr/bin/emacs alias h history alias ll ls -l alias ls ls -F alias rm rm -i

  5. Variables • Creating/Assigning Simple Local variables set {name [= word]}* % set flag % echo $flag % set color = red % echo $color red % set ………… display a list of all local variables cdpath /home/smoon color red … term vt100 user smoon

  6. Variables • Creating/Assigning List Local variables set {name = ([word]*)}* % set colors = ( red yellow green ) % echo $color red yellow green % echo $colors[1] red % echo $#colors 3 % set colors = ( $colors blue ) % echo $colors red yellow green blue

  7. Predefined Local Variables $< the next line of standard input $ argv a list of parameters ($1 = $argv[1]) $ cwd the current working directory $ home shell’s home directory $ noclobber prevents existing files from being overriden by > $ noglob prevents wildcard expandsion $ path used by shell for locating executable files $ prompt shell prompt % cat var.csh # echo -n “please enter your name: “ set name = $< echo hi $name, your current directory is $cwd % var.csh please enter your name: Moon hi Moon, your current directory is /home/smoon

  8. Environment Variables • Creating/Assigning environment variables setenv name word % setenv TERM vt100 % echo $TERM vt100 • Predefined environment variables • $LOGNAME the shell owner’s user ID

  9. Expressions • Supports string, arithmetic, file-oriented • String operators: ==, !=, =~, !~ % cat expr1.csh # echo -n “Do you like C shell?” set reply = $< #get a line of input if ($reply == “yes”) echo you entered yes • Arithmetic operators: -, !, *, /, %, <<, … % cat expr2.csh # set a = 3 set b = 5 if ($a > 2 && $b > 4) echo expression seems to be working

  10. Assigning expression result • You cannot use the set command; use @ • @ variable = expression % set a = 2 * 2 setL Syntax error % @ a = 2 * 2 % echo $a 4 % @ a = $a + $a % echo $a 8 • File-oriented: -option fileName • e: exists, r: has read permission, f: regular file, d: directory, o: owned by the same user …..

  11. Aliases • Customize your own commands via alias alias [word [string]] % alias dir `ls -aF` % dir a.c b.c cc.c UNIX1.ppt UNIX2.ppt % alias dir ls -aF % alias rm `rm -I` % rm a.c delete a.c? No % unalias rm …. Removes all aliases of rm

  12. Useful Aliases • Many people keep the following in .cshrc alias cd ‘cd \!*; set prompt = “$cwd \!>”;ls’ alias rm ‘rm -I’ alias rm ‘mv \!* ~/tomb’ alias h history alias ll ‘ls -l’ % alias cd ‘cd \!*; set prompt = “$cwd \!>”;ls’ % cd . A.c b.c cc.c UNIX1.ppt UNIX2.ppt /home/smoon 2> • To make an alias available to a subshell, place it in the shell’s “.cshrc” file

  13. History • Keeps a record of commands you entered • May be edited or reexecuted later using ! % set prompt = ‘\! %’ 1 % echo FOO FOO 2 % set history = 40 …….. Remember the last 40 commands 40 3 % alias h history 4 % h 1 echo FOO 2 set history = 40 3. alias h history 5 % !1 echo FOO FOO • TC Shell has a more powerful editing features (^p, ^n)

  14. Control Structures • Suitable for high-level programming foreach name ( wordList ) commandList end • Iterates each time with different value for name % cat foreach.csh # foreach color (red yellow green) echo one color is $color end % foreach.csh one color is red one color is yellow one color is green %

  15. Control Structures goto name name: • Jump unconditionally % cat goto.csh # echo gotta jump goto endOfScript echo I will never echo this endOfScript: echo the end % goto.csh gotta jump the end %

  16. Control Structures If (expr) command if (expr1) then list1 switch (expr) else if (expr2) then case pattern: list2 list else breaksw list3 … endif % cat if.csh # echo -n ‘enter a number: ‘ set number = $< if ($number < 0) then echo negative else if ($number = 0) then echo zero else echo positive endif

  17. Control Structures onintr label % cat onintr.csh # onintr controlC while (1) echo infinite loop sleep 2 end controlC: echo control C detected % onintr.csh infinite loop infinite loop ^C control C detected %

  18. Control Structures repeat expr command % repeat 2 echo hi there hi there hi there % while ( expr ) commandlist end % cat multi.csh # set x = 1 while ($x <= $1) echo $x @ x ++ end

  19. Example - junk utility Junk -lp {fileName}* • Replacement of rm; it moves the files into ~/.junk, not removing them; if no .junk, create one. -l lists .junk; -p purges .junk #! /bin/csh case “-l”: set fileList = () # list all specified files set listFlag = 1 set listFlag = 0 # set to 1 if “-l” option breaksw set purgeFlag = 0 # 1 if “-p” option case “-*: set fileFlag = 0 # 1 if at least one file is there echo $arg is an illegal option set junk = ~/.junk goto error breaksw foreach arg ($*) default: switch ($arg) set fileFlag = 1 case “-p”: set fileList = ($fileList $arg) set purgeFlag=1 breaksw breaksw endsw end

  20. Example - junk utility @ total = $listFlag+$purgeFlag+$fileFlag if( $total != 1 ) goto error if( !( -e $junk) ) then if( $filrFlag ) then ‘mkdir’ $junk ‘mv’ $fileList $junk endif exit 0 endif if( $listFlag ) then exit 0 ‘ls’ -lgF $junk error: exit 0 cat << ENDOFTEXT endif Dear $USER, the usage of junk is: junk -p means “purge all files” if( $purgeFlag ) then junk -l means “list junked files” ‘rm’ $junk/* jubk < list of files > exit 0 ENDOFTEXT endif exit 1

  21. Job Control • jobs: displays all of the shell’s jobs • bg %num: resume the specified job in background % man ksh | ul -tdumb > ksh.txt ^Z [1] + stopped man ksh | ul -tdumb > ksh.txt % bg %1 man ksh | ul -tdumb > ksh.txt & • fg %num: resume the specified job in foreground % sleep 1000 & % man ksh | ul -tdumb > ksh.txt & % jobs [2] [1] % fg %ma man ksh | ul -tdumb > ksh.txt &

  22. Built-in Commands • source: execute a script w/o invoking a subshell • Normally, aliases in the script cannot affect the parent shell % vi .login .. Assume we do some editing; normally we have to re-login to see the effect % source .login • The directory stack • pushd [+number|name], popd [+number|name], dirs % pwd /home/smoon % pushd / / ~ % pwd / % popd ~ % pwd /home/smoon

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