Lecture 1: Introduction, Basic UNIX Advanced Programming Techniques

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

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

Logging In Create Acct Cluster PuTTY/SSH Log in Password

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

Unix Filesystem Files Directories Other special files

The Filesystem (eg) / binetchome/tmpusr hollid2scullybinetc netprogunixXlswho

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

Pathname Examples / bin/etc/home/tmp/usr/ Hollid2/scully/bin/local/ netprogunix/Xlswho /usr/bin/ls Syllabus /home/hollid2/unix/Syllabus

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

Viewing files cat less, more od Comparing files diff cmp

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

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

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

File Permissions Three types: readabbreviated r writeabbreviated w execute abbreviated x There are 3 sets of permission: 1. user 2. group 3. other (the world, everybody else)

ls -l and permissions -rwxrwxrwx User Group Others Type of file: - – plain file d – directory s – symbolic link

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

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

Command Options and Arguments command option(s) arguments Options (flags) Short Long Option args Arguments

man Pages man info

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

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

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

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

Shell Variables Values Assignment Reading

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

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

Quoting Escape char Strong quoting Weak quoting

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

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

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

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 Files Zaychik 9472 tweedledee.tgz

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’

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 pts/4 00:00:00 vim pts/4 00:00:00 ps

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

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