Intro to Unix - Day 2

Goals

• use user and group permissions and ownership
• use unix text editors
• learn IO redirection
• learn how to configure your shell
• learn how to configure your PATH and other ENVironmental variables

POST

1. log into the box
2. start a terminal
3. where are you?
4. view a directory listing to see what's there
5. Create a file called "postfile.txt" (no quotes)
6. Make a copy of the file called "postcopy.txt"
7. make a [sub]directory under your home directory called "postdir"
8. move the postcopy.txt file to the new directory
9. from your home directory, show a listing of the files in the new directory. Leave the listing on your screen as evidence of your work.
10. You are victorious; celebrate in the endzone.

Permissions and Ownership

• view a listing of your current dir
• eyeball the chart on page 384. What can you tell about the files in your dir?
• Understanding permissions: owners
• Understanding permissions: groups
• Understanding permissions: other folks

• Directory permissions are a bit different: r=list, w=add remove delete rename, x=cd to the dir or execute.
• Bonus: advanced weirdness: setuid, setgid, sticky bits. p386.

setting permissions

• symbolic names: u=user, g=group, o=others, a=all others (default).
  + = add to existing, - = delete from existing, "=" = set explicitly to stated value only. pp.391-393
• octal: 4=read, 2=write, 1=execute

changing groups and owner

• changing a group ownership: chgrp [group] [target]. Can use -R recursion.
  Can see your groups with groups or id.
• changing owner: chown [user] [target]. Can use -R recursion.
• Some systems will allow compound user-group assignment: chown [user].[group] [target.
• Default file-creation permissions: umask. umask is the complement of octal default chmod permissions, dirs: 777 - 022 = 755. Files 666 - 022 = 644. You can be as lax or paranoid as you want to be. Look ahead: setting umask in your login defaults.

Becoming someone else...

• The wonders of su (dash) pp.370-71.

  Highlight p. 370

• The extended wonders of sudo

editing!

• Pico - easiest to learn, very limited. Bundled with pine MUA. You will outgrow pico very soon.
  1. pico picofile: starts a file called picofile
  2. mary had a little lamb: enters text into the file
  3. [ctrl-o]: writes Out
  4. [ctrl-x]: eXits the program
• vi - always available, exceedingly powerful, maddening to learn. Most notable characteristic: two-mode operation (insert and command).
  1. vi vifile: starts a file called vifile
  2. i: enters Insert mode
  3. Mary had a little lamb: enters text into the file
  4. [esc]: toggles mode (now in command mode)
  5. :wq: Writes and Quits the file
• emacs - Byzantine complexity, easily and frequently extended for complex apps like news readers, programming IDEs, etc. Most notable characteristic: large size and extensive use of multi-key sequences. p.627+
  1. emacs emacsfile: starts a file called emacsfile
  2. mary had a little lamb: inserts text into the file
  3. [ctrl-x][ctrl-s]: Saves file
  4. [ctrl-x][ctrl-c]: Closes the file and quits

Introduction to unix utilities

• echo: spray out some text from the command line
• cat: spray out some text from a file (cf. DOS type)
• more: a "paging" utility (cf. less)
• grep: find strings in text
• find: find strings in text (needs a default action like -print) p187-97

redirection

• a quick example: ls -l > ls_output.txt
• | : pipe; run output of one util into the input of another
• >: redirect output to a file (overwrite)
• >>: redirect output to a file (append)
• <: redirect input from a file
• /dev/null
• find . -name txt 2> /dev/null

shell configuration

• .profile Bourne and variants (sh, bash, ksh, etc)
• .cshrc C shell
• .login C shell
• .logout C shell
• .forward forwards your mail
• .plan/.project finger information
• .signature email and other sigs
• .exrc controls default vi behavior (ex for historical reasons)
• .login C shell

altering the ENVironment

• Bourne-like: export [variable]=[value]
• Cshell: setenv [variable] [value]
• EDITOR editor definition (also VISUAL), will be read by apps that require invocation of a text editor.
• PATH search path for executables
• TERM terminal emulation: VT100 and ANSI are safe, boring examples

Homework

• read news:comp.unix.questions
• read news:comp.unix.shell
• elementary job control p423-25
• other unixy utilities p494-5, 505-07, 520-22, 526-27.

Remember, your login is based on your machine's hostname, not on any other number.
~/[initials] refers to the subdirectory under your homedir, named after your initials. Everything except for .dotfiles will be stored in your ~/[initials] directory.