UNIX Basics

1. UNIX Basics UNIX Basics CIS 218 Oakton Community College

2. UNIX was invented in 1969 at AT&T Bell Labs Ken Thompson and Dennis Ritchie are credited as the original architects and developers of “C”. Written in the C programming language in 1973 Resold under UNIX System License (USL) Current USL version SystemV R4 Different commercial flavors: Solaris (Sun), AIX (IBM), Irix (SGI), HPUX (Hewlett Packard), SCO Academic version – BSD (Mac OS X base) UNIX Variants – LINUX, UNIX “ports” – Android, MAC OSX History

3. Unix Design UNIX Design • Modularity • Each part of the Unix system is a system unto itself • printing, networking, mail, file management, accounting, etc. • Many Unix systems can be run in different modes. This allow for a certain set of modules to be run based on usage (workstation, server). • UNIX utilities are independently developed packages

4. UNIX Layers

5. UNIX Versus DOS/Windows • UNIX – everything is a file • UNIX is case sensitive, DOS is not • UNIX searches $PATH for executables, DOS starts in current directory, then PATH. • UNIX is multi-user, DOS is not. Windows is (kind of) • UNIX GUI sits “on top of” the OS - same as Windows thru ME). This changed After NT. • UNIX directory has one starting point – root “/”. Windows has multiple A:, C:, D: etc.

6. UNIX Versus DOS/Windows • DOS UNIX Command Description • CD pwd Display current directory • CD \ cd / Moves to the root directory • CD .. cd .. Moves up one level in the directory structure • CD path cd path Sets the current directory to a new directory • CHKDSK du Displays disk usage • CLS clear Clear the screen • COMMAND sh, csh .. Start a new shell (command processor) • COMP cmp Compares two files and shows the difference • COPY cp Copy a file • DATE date Displays the date • DEL or ERASE rm Deletes a file • DELTREE rm -r Deletes a directory tree ( CAREFUL ! ! ! ) • DIR ls -l Lists the directory in a long format • DIR /W ls Lists the directory in a short format • ECHO echo Displays a message or a variable • EXIT exit End a shell • FC diff Displays differences between two files • FIND grep Displays lines matching a given pattern • HELP man Display information about a command • MD or MKDIR mkdir Creates a directory • MORE more Displays text a page at a time • MOVE mv Moves a file • PRINT lpr Prints a file • RD or RMDIR rmdir Removes a directory • REN mv Renames a file • SET set Sets a variable to a given value • SORT sort Sorts a data • TIME date Displays the time • TYPE cat Displays a file

7. Shell – “sh” original interface to UNIX Bourne Shell added some desirable features but has different syntax for some things Newer Bourne Shell variants are Korn Shell (ksh) and Born Again Shell (bash) C Shell – C program language syntax, tcsh, Perl – Program Extract and Reporting Language Some systems allow user to chose which shell you prefer with “chsh”. The full path to the shell must be given Shells

8. When you log in to interact with UNIX, you see a “shell prompt” ($ or %) A “word” is a text string separated by white space – space, Tab or IFS The shell is a program that runs constantly and executes the commands you give it A command is the first “word” on a line. All following words are command line parameters Commands terminators: “<LF>” – Enter or Return, “;”, “|”, “>” The Shell

9. UNIX command line • You interact with the Unix by entering commands. • The basic form of any Unix command is: Command Option(s) Argument(s) • Most commands provide integral help or on-line Manual (man page) • Options or flags modify the way that a command works. They usually consist of a hyphen followed by a single letter.

10. Unix file types • Directory - holds other files or directories. • Normal Files Text files - text that is “human readable”. Binary files - executable files • Link - allows space efficient copying of files/directories. Symbolic or “soft” - may span file systems. Hard - is indistinguishable from the original file/directory. • Hidden File - any file that begins with a “.” (dot). • Character or Block Special Files – hardware interface. • “virtual” files – pipes, semaphores, sockets.

11. UNIX uses a single hierarchy to store files beginning with root “/” Files are a named collection of bytes Directories contain other files (or not) Files and Directories juliana Project File1 File2 File3

12. • Home directory (~ ) - top of your file tree: • Root directory (/ ) - top of a file tree: • Current directory (.) - directory you’re in now (pwd) • Dot (.) - current directory • Dot-dot (..) - parent of current directory • Path - Where to find file or directory Absolute path: /fs/scd/home0/juliana/myfile Relative path: ./myfile • “Standard files” – STDIN, STDOUT, STDERR Basic Directory Terms

13. cd - change directories (built into shell) pwd – present working directory mkdir - creates a directory rmdir - removes a directory (must be empty first) rm myfile1 - remove a file rm -fr - removes directory and everything below touch <filename> - creates an empty file cat <filename> - displays a file on screen more <filename> - to see a screenful at a time • mv myfile1 myfile2 - renames (moveas) a file Managing Files and Directories

14. Tar stands for “tape archive” but is more often used to gather files into one bundle. Equivalent of a ZIP file, without the compression. - cd to the directory above the one you want to archive tar cvf - diry_name > diry.tar - To “list” the archive, use tar -xvf diry.tar - To “untar” the archive, use tar -xvf diry.tar - Compressed files take up less space. To compress a tar file, use compress diry.tar or gzip diry.tar - To uncompress, use uncompress diry.tar.Z or gunzip diry.tar.gz - Note equivalent gzip commands: zcat, zgrep, zmore, zdiff Tar and Compress

15. You “own” your files and directories user-group-other read/write/execute permissions -rw-r--r-- 1 jsmith staff 164870 27 Feb 17:58 6.bmp -rw-r--r-- 1 jsmith staff 164870 27 Feb 17:57 5.bmp + to add, - to remove alphabetic permissions r=4, w=2, x=1 so rwx: 4+2+1=7 for numeric chmod command changes permissions chmod 604 6.bmp chmod g-rw 6.bmp -rw----r-- 1 jsmith staff 164870 27 Feb 17:58 6.bmp File Permissions

16. File Permissions • Access rights on files. r : indicates read permission (or otherwise), that is, the presence or absence of permission to read and copy the file w : indicates write permission (or otherwise), that is, the permission (or otherwise) to change a file x : indicates execution permission (or otherwise), that is, the permission to execute a file, where appropriate • Access rights on directories. r : allows users to list files in the directory; w : allows users to delete files from the directory or move files into it; x : allows users the right to access files in the directory (e.g. cd into directory), read files in the directory provided you have read permission on the individual files.

17. File Permissions

18. What’s in my directory? • ls db5-24 nwade.txt schumacher5-19.txt kirsh5-12.txt nwade5-13a.txt sheu5-20.txt • ls -alt -rw-r--r-- 1 jsmith staff 712 24 May 09:12 db5-24 -rw-r--r-- 1 jsmith staff 1660 12 May 12:12 kirsh5-12.txt -rw-r--r-- 1 jsmith staff 3610 11 May 08:16 ming.txt -rw-r--r-- 1 jsmith staff 2444 10 May 16:53 mingrep • Wildcard - * stands for any (# of) character(s) • Wildcard - ? stands for any single character • [abcde…] selection set, any single character within the brackets User Commands for Files

19. wc - word, line, character, and byte count echo - echo characters back (print) sort - sort lines of a text file uniq – remove consecutive duplicats lines cut/paste/join – manipulate data by physical location in a record or file sed – stream editor, vi commands in a batch file awk – string manipulation tr – translate from one character to another strings – review a binary file for text od – examine a file for binary contents head, tail – display begin and end of a file cat – copy to stdout cp – copy a file User Commands for Files

20. diff – find differences between two text files find - a tricky but useful command find . -name myfile -print find . -name ‘*name*’ –print –exec “cmd” {} \; • grep - stands for “general regular expression print” Search all files for a pattern: grep -i “lightning system” * grep -v “lightning system” * grep -c “gee whiz” * Finding and Searching

21. Wildcard characters • Wildcard characters can be used to represent many other characters in listing filenames. • Use them whenever you need to define a string of characters, such as a filename, for use with a command. • Useful wildcards are: * matches any characters, zero or more. ? match any single character. [...] matches any character in the enclosed list or range. Examples: • ls *.txt # Lists all the files in the current directory # that have the extension .txt. • cat memo? # Concatenate files that start with “memo” # and are followed by any one character. • rm part[1-3] # Remove files: part1, part2 and part3

22. By default, a terminal keyboard is the standard input file (STDIN) from which to read in information Terminal is also the standard output file (STDOUT) to which information is sent from the command. Input can be given from the command line, or from a file: a.out < inputfile Output goes to your screen, or you can “redirect” it to a file: echo “hi there” > out.file • To append, use >> echo “hi back at you” >> out.file • “here” document for inline stdin << EOF • Use the “tee filename” command to redirect out put to both STDOUT and a file. Input/Output (I/O) and Redirection

23. Input/Output (I/O) and Redirection • “<& m” Duplicates standard input from file descriptor m • “[n] >& m” Duplicates standard output or file descriptor n if specified from file descriptor m i.e. 2>&1 • “[n] <&-” Closes standard input or file descriptor n if specified • “[n] >&-” Closes standard output or file descriptor n if specified. • “|” or pipe (prior slide) is also redirection. It redirects STDOUT from the preceding command to STDIN of the following command. The general term for the following command is called a filter as it modifies or filters the output of the preceding command..

24. You can string commands together into a single command using pipes ( | ) ps | grep juliana - what am I running now • Save the results in a file: “who | wc > usercount” • Used with file manipulation commands as “filters” “who | wc” - count how many users on the system Pipes

25. System Uptime uptime What time is it? date • Where is a command? which ls whereis ls • How do I use a command? man ls System Info Commands

26. Where am I? pwd - print working directory cwd - current working directory Who am I? whoami Who is on the system? What’s running? who, w ps –ef, -aux System Info Commands

27. passwd - change password chsh – change default shell lpr - print a file (printer at OCC) history - (C shell builtin) - list of previous commands alias - create a pseudonym or shorthand for a command (behaves differently for C versus Bourne shell) More Useful Commands, cont.

28. Front end to ed Universal among UNIX and it’s variants vi somefilename (copies file into memory buffer) Three modes – command mode, text mode(Esc), operator line(:) determines how keystrokes are interpreted by vi Editing - vi

29. Editing – vi (commands) • i – insert text • x – delete a character • r – replace a character • R – replace text • yy p – copy a line • dd – delete a line • /text – locate text • / - repeat last find • <Enter> or <Return> - ends a line • :wq – save results and quit (:wq! – force overwrite of file) • :q - quit (no save) • Navigation: arrow keys or HJKL