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Unix Shell Environments

Unix Shell Environments. September 27, 2004 Class Meeting 6, Part I. * Notes adapted by Lenwood Heath from previous work by other members of the CS faculty at Virginia Tech. Shell Characteristics. Command-line interface between the user and the operating system

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Unix Shell Environments

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  1. Unix Shell Environments September 27, 2004 Class Meeting 6, Part I * Notes adapted by Lenwood Heath from previous work by other members of the CS faculty at Virginia Tech

  2. Shell Characteristics • Command-line interface between the user and the operating system • Automatically starts on login, waits for user to type in commands • Both a command interpreter and a programming language • Shell script is a text file containing logic for shell interpretation Lenwood Heath, Virginia Tech, Fall, 2004

  3. Shell Interactivity • Command line parsing • Environment • Textual completion • Aliases • Command line editing • Command history • Configuration Lenwood Heath, Virginia Tech, Fall, 2004

  4. Shell Programming • Variables • Control structures • Loops and conditionals • Function definition and invocation • Shell scripts • Next lecture Lenwood Heath, Virginia Tech, Fall, 2004

  5. Various Unix Shells • sh (Bourne shell, original Unix shell) • ksh (Korn shell) • csh (C shell, developed at Berkeley) • tcsh • bash (Bourne again SHell) • Default user shell in Linux • http://www.faqs.org/faqs/unix-faq/shell/shell-differences/ Lenwood Heath, Virginia Tech, Fall, 2004

  6. Bourne Again SHell • bash is the standard shell for this class • Superset of the Bourne shell (sh) • Borrows features from sh, csh, tcsh, and ksh • Part of the GNU project Lenwood Heath, Virginia Tech, Fall, 2004

  7. Environment Variables • A set of variables the shell uses for certain operations • Variables have a name and a value • Current list can be displayed with the env command • Send value of varname to standard output with echo $varname Lenwood Heath, Virginia Tech, Fall, 2004

  8. Environment Variable Examples • [cs2204@acorn bin]$ echo $PS1 [\u@\h \W]\$ • [cs2204@acorn bin]$ echo $PATH /usr/local/bin:/bin:/usr/X11R6 bin:/usr/games:/home/courses/ cs2204/bin Lenwood Heath, Virginia Tech, Fall, 2004

  9. Setting Environment Variables • Set variable with varname=value • PS1=$USER@$HOSTNAME: • Change default shell prompt • PS1="bash rules> " • PATH=$PATH:$HOME/bin • Append :$HOME/bin to PATH • PATH=$PATH:~:. • Append :~:. to PATH • DATE=`date` or DATE=$(date) • Capture output from date command Lenwood Heath, Virginia Tech, Fall, 2004

  10. Textual Completion • <tab> attempts to complete the current command or filename • pus<tab> expands to pushd<space> • pu<tab> gives the alternatives pu pup pushd • In /etc, entering ll modu<tab> gives modules modules.conf modules.devfs [cs2204@blackberry etc]$ ll modules Lenwood Heath, Virginia Tech, Fall, 2004

  11. Aliases • alias shortcut=command • Examples • alias pu=pushd • alias po=popd • alias l="ls –F –C" • alias ll="ls –L –l –F" • alias d=dirs • alias hide="chmod og-rwx" • alias unhide="chmod og+r" Lenwood Heath, Virginia Tech, Fall, 2004

  12. Command History • Use history command to list previously entered commands • Use fc –l <m> <n> to list previously typed commands from m through n • Use up and down cursor keys to scroll through history list Lenwood Heath, Virginia Tech, Fall, 2004

  13. Editing on the Command Line • bash provides a number of line editing commands • Default emacs-mode commands • Esc-b Move back one word • Esc-f Move forward one word • Ctrl-a Move to beginning of line • Ctrl-e Move to end of line • Ctrl-k Kill text from cursor to end of line Lenwood Heath, Virginia Tech, Fall, 2004

  14. Login Scripts • Startup scripts executed at login • /etc/profile • ~/.bash_profile • ~/.bash_login (if no .bash_profile) • ~/.profile (if neither are present) • ~/.bashrc • Script executed upon logout • ~/.bash_logout Lenwood Heath, Virginia Tech, Fall, 2004

  15. Example .bash_profile (partial) # .bash_profile # include .bashrc if it exists if [ -f ~/.bashrc ]; then . ~/.bashrc fi # Set variables for a warm fuzzy environment export CVSROOT=~/.cvsroot export EDITOR=/bin/vi export PAGER=/usr/bin/less Lenwood Heath, Virginia Tech, Fall, 2004

  16. Example .bashrc (partial) # .bashrc # abbreviations for some common commands alias bye=logout alias h=history alias l='ls -F -C' alias ll='ls -L -l -F' alias po=popd alias pu=pushd Lenwood Heath, Virginia Tech, Fall, 2004

  17. interactive shell interactive shell interactive shell Login and Other Shells login shell /etc/profile~/.bash_profile~/.bashrc ~/.bashrc ~/.bashrc ~/.bashrc Lenwood Heath, Virginia Tech, Fall, 2004

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