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UNIX Tools G22.2245-001, Fall 2000

Overview of shell core functionality, features of /bin/sh, /bin/ksh, and /bin/csh, including simple and complex commands, input/output redirection, pipes, wildcards, command substitution, background processes, shell variables, and more.

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UNIX Tools G22.2245-001, Fall 2000

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  1. UNIX ToolsG22.2245-001, Fall 2000 Danielle S. Lahmani email: lahmani@cs.nyu.edu Lecture 4 2000 Copyrigths Danielle S. Lahmani

  2. Overview • shell core functionality • /bin/sh • /bin/ksh • /bin/csh 2000 Copyrigths Danielle S. Lahmani

  3. Shell Core Features • Simple and complex commands • redirection of input/output • pipes • wildcards • command substitution • background processes • shell variables • here documents • built-in cmds • programming constructs 2000 Copyrigths Danielle S. Lahmani

  4. The Korn Shell: /bin/ksh • Supports all features described in the Bourne shell (/bin/sh) • Alias mechanism • History mechanism for access of previous commands • Functions • Enhanced job control • Arithmetic • Tilde substitution 2000 Copyrigths Danielle S. Lahmani

  5. The Korn shell: /bin/ksh STARTUP FILES: • /etc/profile • $HOME/.profile • ALIAS: • alias [-tx] [word[=string]] • alias -x : to export alias to child shell • unalias aliasname: to remove an alias 2000 Copyrigths Danielle S. Lahmani

  6. /bin/ksh: History Mechanism • Numbered commands $ PS1='!!’ /* set prompt to contains a ! */ $HISTSIZE default is 128 • using the built-in vi editor • declare VISUAL=vior EDITOR=vi • to edit current line, press ESC key to enter the editor • vi cmds to edit line, when done, press ESC key again, • additional movement: cursor up(k or - ) cursor down (j or +) • additional searching /string or ?string : searches backward and forward through history, respectively. 2000 Copyrigths Danielle S. Lahmani

  7. /bin/ksh (continued) • ARITHMETIC: Usinglet expression • TILDE SUBSTITUTION • ~ $HOME • ~user home directory of user • ~/pathname $HOME/pathname • ~+ $PWD • ~- $OLDPWD 2000 Copyrigths Danielle S. Lahmani

  8. /bin/ksh: FUNCTIONS • Allows functions that may be invoked as shell commands function name { list of commands } or name() { list of commands } 2000 Copyrigths Danielle S. Lahmani

  9. /bin/ksh: Functions (continued) • can use parameters • returning from a function • local variable using typeset • functions can be recursive 2000 Copyrigths Danielle S. Lahmani

  10. /bin/ksh: ENHANCED JOB CONTROL • jobs list your jobs • bg places a specified job in the background • fg places a specified job in the foreground • kill sends an arbitrary signal to a process or job • ^z to stop a foreground job • stop to suspend a background job 2000 Copyrigths Danielle S. Lahmani

  11. /bin/ksh: coprocess PIPES • |& operator supports a simple form of concurrent processing • cmd |& cmd run as a background process whose standard input and output channels are connected to the original parent shell via a two way pipe. 2000 Copyrigths Danielle S. Lahmani

  12. The C Shell: /bin/csh • Supports all features described in the Bourne shell • simple and list variables • Alias mechanism with arguments • History mechanism for access of previous commands • Enhanced job control • Arithmetic • directory stack 2000 Copyrigths Danielle S. Lahmani

  13. /bin/csh: STARTUP FILES • $HOME/.cshrc • /etc/.login • $HOME/.login 2000 Copyrigths Danielle S. Lahmani

  14. /bin/csh: simple variables • set { name [=word]} * • access • $(name) • ${name} • ${?name} replaced by 1 if name is set, 0 otherwise 2000 Copyrigths Danielle S. Lahmani

  15. /bin/csh: list variables • Variables to which you can assign a list of values • set { name = ( {word}*) } * • Access: • $name[selector] • ${name[selector]} selector can be a range • $#name • ${#name} number of elements in name 2000 Copyrigths Danielle S. Lahmani

  16. /bin/csh: predefined local variables • $< the next line of standard input fully quoted • $noclobber prevents existing files from being overridden by >, and non-existent files from being appended to by >> • $noglob prevents wildcard expansion 2000 Copyrigths Danielle S. Lahmani

  17. /bin/csh: methods for accessing C shell arguments • $argv a list that contains all of the positional parameters, same as $* • $argv[1] is equal to $1 • $#argv number of arguments • $argv[1-n] arguments 1 through n • $argv[0] illegal, must use $0 • $argv[$#argv] last argument  2000 Copyrigths Danielle S. Lahmani

  18. /bin/csh:file inquiry operator • -option filename operator meaning r read access w write access x execute access e existence o ownership z zero length f plain file d directory 2000 Copyrigths Danielle S. Lahmani

  19. /bin/csh: ARITHMETIC EXPRESSION • Assignment of results of an expression: • Set variable to expression @ variable op expression @ variable[index] op expression • example: @ x = 2 + 3 %echo $x 5 2000 Copyrigths Danielle S. Lahmani

  20. /bin/csh:ALIAS • alias [word[string]] • unalias • to share an alias with other subshells, place it under .cshrc 2000 Copyrigths Danielle S. Lahmani

  21. ARGUMENTS IN ALIASES • C shell assumes that all arguments come at the end of the alias definition, unless you specify otherwise • Example • % alias cx chmod +x • % cx * # makes files in all current directory executable • Two common arguments designations to pass arguments to aliases 2000 Copyrigths Danielle S. Lahmani

  22. /bin/csh alias examplereference: The Unix C shell field Guide G, Anderson P. Anderson • find requires a single argument, we must escape ! to suppress interpretation from the C shell %alias loc 'find ~ -name \!^ -print' %loc ttydoc77 % alias ldir 'ls -l \!* | grep "^d"' % ldir ../utils /usr/bin 2000 Copyrigths Danielle S. Lahmani

  23. /bin/csh: history mechanism • For numbered commands • set prompt = '\! %’ • storage of commands • set history = 40 size of history file • set savehist=32 save 32 commands across sessions 2000 Copyrigths Danielle S. Lahmani

  24. /bin/csh: hist mech (continued) • command reexecution • !! reexecute previous command • !number • !prefix • !?substring • command editing • %!even :s/pat1/pat2 substitute pat1 with pat2 • %^pat1^pat2 reexecution of previous command substituting pat1 with pat2 2000 Copyrigths Danielle S. Lahmani

  25. ACCESS PORTION OF A FILENAME • Modifier part of file portion of filename returned • :h head filename minus trailing path • :r root filename minus trailing *.suffix • :e extension trailing .* suffix • :t tail filename minus leading dir path 2000 Copyrigths Danielle S. Lahmani

  26. /bin/csh: CONTROL STRUCTURES • foreach ……. end • if then else endif • switch case … endsw • while … end • onintr [-l label] allows to specify a label to jump to when shell receives a SIGINT 2000 Copyrigths Danielle S. Lahmani

  27. /bin/csh: PIPING • Process1 |& process2 • Redirects standard output and standard error from process 1 to process 2 2000 Copyrigths Danielle S. Lahmani

  28. /bin/csh:MULTIPLE REDIRECTION • Cmd >& file send both standard output and standard error to file • Cmd >&! file same as above, even in noclobber is set • Cmd >>& file append standard error and standard output to end of file • Cmd1 | & cmd2 pipe standard error together with standard output • (cmd > file1) >& file2 send standard output to file1; send standard error to file2 2000 Copyrigths Danielle S. Lahmani

  29. /bin/csh: JOB CONTROL • Same as ksh, plus • stop suspend background process • suspend suspend foreground process • notify notify when current job changes status 2000 Copyrigths Danielle S. Lahmani

  30. /bin/csh: DIRECTORY STACK • pushd[+number|name] pushd pushes the directory onto the directory stack • popd [+number] popd pops a directory from the directory stack • dirs: lists the current directory stack . 2000 Copyrigths Danielle S. Lahmani

  31. Effective and efficient shell progreference: Unix shell Tutorial G.Snyder J.R. Mashey Bell Labs • Minimize number of processes generated • Find out which cmds are built-in and which are not. • Number of data bytes accessed • Minimize Directory searches • Optimize Directory search order and the PATH variable • Minimize arithmetic and character processing • Avoid command substitution when you can • Move loop invariant outside of loop, especially for command substitution 2000 Copyrigths Danielle S. Lahmani

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