Lecture 1: Introduction, Basic UNIX

1. Lecture 1: Introduction, Basic UNIX Advanced Programming Techniques

2. Why are we here? • What’s a computer • Why do we run programs? • What is needed to create a program?

3. Applications Shell \ Kernel (OS) Hardware Structure of a typical OS • There are many standard applications: • file system commands • text editors • compilers • text processing

4. Logging In • Create Acct • www.cs.drexel.edu/Account.php • Cluster • PuTTY/SSH • Log in • Password

5. Home Directory • The user’s personal directory. E.g., • /home/kschmidt • /home/vzaychik • Location of many startup and customization files. E.g.: .vimrc .bashrc .bash_profile .forward .signature .plan .logout

6. Unix Filesystem • Files • Directories • Other special files

7. / bin etc home/ tmp usr hollid2 scully bin etc netprog unix X ls who The Filesystem (eg)

8. Pathnames • Unique, on a given filesystem • Absolute vs. relative • ./ ../ ~/

9. Pathname Examples / bin/ etc/ home/ tmp/ usr/ Hollid2/ scully/ bin/ local/ netprog unix/ X ls who Syllabus /usr/bin/ls /home/hollid2/unix/Syllabus

10. Commands for Traversing Filesystem • ls • pwd • cd • rm • cp • mv • mkdir • rmdir

11. Viewing files • cat • less, more • od • Comparing files • diff • cmp

12. Copying, removing, linking • rm – remove file • mv – move (rename) file • cp – copy file • ln – create hard (inode) or soft (symbolic) links to a file • touch – update file modification time, create an empty file if file doesn’t exist

13. Commands for directories • mkdir make directory • rmdir remove directory • Directories can also be moved or renamed (mv), and copied (cp –r)

14. Commands for Archiving • tar – Tape Archive • makes a large file from many files • gzip, gunzip • compression utility • tar on Linux does compression with the z option: $ tar czf 571back.tgz CS571 $ tar xzf assn1.tgz

15. File Permissions • Three types: • read abbreviated r • write abbreviated w • execute abbreviated x • There are 3 sets of permission: • user • group • other (the world, everybody else)

16. ls -l and permissions -rwxrwxrwx UserGroup Others Type of file: - –plain file d –directory s – symbolic link

17. Bourne-again Shell (bash) • Shells • Startup • Upon login (interactive), at the shell prompt • customization files: • /etc/profile • .bash_profile • .bashrc

18. Command syntax • First token is the “command” • Come in 3 flavors: • alias • shell builtin • External programs (utilities) • $PATH • Use type

19. Command Options and Arguments commandoption(s) arguments • Options (flags) • Short • Long • Option args • Arguments

20. man Pages • man • info

21. Some simple commands • date – print current date • who – print who is currently logged in • finger usr – more information about usr • ls -ao – lists (long) all files in a directory • du -sh – disk usage summary, human readable • quota

22. Standard I/O • The shell establishes 3 I/O channels: • stdin (0) • stdout (1) • stderr (2) • These streams my be redirected to/from a file, or even another command

23. Basic control codes • Ctrl-D (^D) • set ignoreeof • Ctrl-C (^C) • Ctrl-U (^U) • Ctrl-Z (^Z) • Ctrl-L (^L)

24. Shell metacharacters • Some characters have special meaning to the shell: • I/O redirection < > | • wildcards * ? [ ] • others & ; $ ! \ ( ) space tab newline • These must be escaped or quoted to inhibit special behavior

25. Shell Variables • Values • Assignment • Reading

26. Shell maintains variables • Some common ones: $PATH – list of directories to search for utilities $PS1 – Primary prompt $HOME – user’s home directory $USER – user’s login name $PWD – current working directory

27. set command (shell builtin) • The set command with no parameters will print out a list of all the shell variables • Sets options in the shell • -o • -noclobber • -ignoreeof

28. Quoting • Escape char • Strong quoting • Weak quoting

29. I/O Redirection • > - output to a file (clobber) • >> - append • < - input from a file • 2> - redirect stderr

30. Pipes – connecting processes • A pipe is a holder for a stream of data. • A pipe can be used to hold the output of one program and feed it to the input of another. prog1 prog2 STDOUT STDIN

31. filters • Programs that read some input (but don’t change it), perform a simple transformation on it, and write some output (to stdout) • Some common filters… • wc – word count (line count, character count) • tr – translate • grep, egrep – search files using regular expressions • sort – sorts files by line (lexically or numerically) • cut – select portions of a line • uniq – Removes identical adjacent lines • head, tail – displays first (last) n lines of a file

32. The Unix Philosophy • Stringing small utilities together with pipes and redirection to accomplish non-trivial tasks easily • E.g., find the 3 largest subdirectories: $ du –sh * | sort –nr | head -3 120180 Files 22652 Zaychik 9472 tweedledee.tgz

33. pipes and combining filters • Connect the output of one command to the input of another command to obtain a composition of filters • who | wc -l • ls | sort -f • ls -s | sort -n • ls -l | sort -nr -k4 • ls -l | grep ‘^d’

34. Process Control • Processes run in a subshell • Subshells inherit exported variables • Each process is has an ID (pid) and a parent (ppid) • Use the ps utility to look at some processes: $ ps PID TTY TIME CMD 350 pts/4 00:00:00 bash 22251 pts/4 00:00:00 vim 22300 pts/4 00:00:00 ps

35. Job Control • The shell allows you to manage jobs • place jobs in the background • move a job to the foreground • suspend a job • kill a job

36. Editors • A text editor is used to create and modify text files. • The most commonly used editors in the Unix community: • vi (vim on Linux) • $ vimtutor • emac • $ emacs • Then, hit ctrl-h t (that’s control-h, followed by ‘t’) • You must learn at least one of these editors