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UNIX Basics. UNIX Basics CIS 218 Oakton Community College. 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)

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unix basics

UNIX Basics

UNIX Basics

CIS 218

Oakton Community College

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 design
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
unix versus dos windows
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 windows1
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
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, “;”, “|”, “>”

The Shell
unix command line
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.
unix file types
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.
files and directories
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






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

Basic Directory Terms
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

Managing Files and Directories
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

Tar and Compress
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
file permissions1
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.

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
user commands for files1
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
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” *

Finding and Searching
wildcard characters
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.


        • 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
input output i o and redirection1
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..
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


What time is it?


• Where is a command?

which ls

whereis ls

• How do I use a command?

man ls

System Info Commands
system info commands1
Where am I?

pwd - print working directory

cwd - current working directory

Who am I?


Who is on the system? What’s running?

who, w

ps –ef, -aux

System Info Commands
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)

More Useful Commands, cont.
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
editing vi commands
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