UNIX Basics UNIX Basics CIS 218 Oakton Community College
History 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
UNIX Unix Design 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
UNIX Layers
UNIX Versus DOS/Windows UNIX everything is a file UNIX is case sensitive, DOS is not UNIX searches $PATH for executables, DOS starts in current directory, then PATH. UNIX is multi-user, DOS is not. Windows is (kind of) UNIX GUI sits on top of the OS - same as Windows thru ME). This changed After NT. UNIX directory has one starting point root /. Windows has multiple A:, C:, D: etc.
UNIX Versus DOS/Windows DOS UNIX Command Description CD pwd Display current directory CD \ cd / Moves to the root directory CD.. cd.. Moves up one level in the directory structure CD path cd path Sets the current directory to a new directory CHKDSK du Displays disk usage CLS clear Clear the screen COMMAND sh, csh.. Start a new shell (command processor) COMP cmp Compares two files and shows the difference COPY cp Copy a file DATE date Displays the date DEL or ERASE rm Deletes a file DELTREE rm -r Deletes a directory tree ( CAREFUL!!! ) DIR ls -l Lists the directory in a long format DIR /W ls Lists the directory in a short format ECHO echo Displays a message or a variable EXIT exit End a shell FC diff Displays differences between two files FIND grep Displays lines matching a given pattern HELP man Display information about a command MD or MKDIR mkdir Creates a directory MORE more Displays text a page at a time MOVE mv Moves a file PRINT lpr Prints a file RD or RMDIR rmdir Removes a directory REN mv Renames a file SET set Sets a variable to a given value SORT sort Sorts a data TIME date Displays the time TYPE cat Displays a file
Shells Shell sh original interface to UNIX Bourne Shell added some desirable features but has different syntax for some things Newer Bourne Shell variants are Korn Shell (ksh) and Born Again Shell (bash) C Shell C program language syntax, tcsh, Perl Program Extract and Reporting Language Some systems allow user to chose which shell you prefer with chsh. The full path to the shell must be given
The Shell When you log in to interact with UNIX, you see a shell prompt ($ 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, ;,, >
UNIX command line You interact with the Unix by entering commands thru thee shell. The line is parsed as text sepaated by whitspace caracters into words or tokens. The first word is always a command. 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.
Unix file types (ls l) d: Directory - holds other files or directories. -: Normal Files Text files - text that is human readable. Binary files - executable files l: 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). c,b: Character or Block Special Files hardware interface. virtual files pipes, semaphores, sockets.
Files and Directories UNIX uses a single hierarchy to store files beginning with root / Files are a named collection of bytes juliana Project File1 File2 File3 Directories contain other files (or not)
Basic Directory Terms 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
Managing Files and Directories 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
Tar and Compress - 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
File Permissions 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 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.
File Permissions Symbol Meaning u user g group o other a all r read w write (and delete) x execute (and access directory) + add permission - take away permission
User Commands for Files 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 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
Finding and Searching 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 *
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
Input/Output (I/O) and Redirection 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 <& 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..
Pipes 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
System Info Commands 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 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
More Useful Commands, cont. 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)
Editing - vi 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 (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