Unix Basics

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Unix basics

File types

1.ordinary files – contains text or image does not have any other files in it

2.directories – branching points in hierarchy level directory tree. May contain other files , special files, other directories

3.special files – any devices connected to unix like(tape drives,printer, and terminal)

                By default unix consider terminal as stdin as well as stdout(standard input and output)

                Special files are normally stored under the directory /dev

4.pipes – temporary file used to link two commands together. (E.g) cat jai1.txt|more output of cat command is stored in a temp file pipe and sent to more command as input.

Symbol	File type
-	Normal file
D	directory
|	Symbolic link
B	Block device file
C	Character device FILE
P	FIFO or named pipe

File names

Unix file name can be upto 256 char, allows to use most char except spaces, tab spaces, and special symbols, unix is case sensitive.

Extensions can be used to identify the type of files.

.a archive file

.c c program fiile

.f forton file

.o object/executable file

.z compressed file

Hidden files begin with .(dot) example .login .mailrc .mwmrc

File names are unique that is under one directory two files cant have the same name.

Path names:

Path – location of a specific file or folder

Types of pathname

                1.absolute pathname -  starts with the root folder /

                2.relative path name – does not start with root folder (E.g) ../bin ~/proj/rep.text

 Unix commands:

                OS is a set of programmed instruction that tells how to work.

An user interaction with OS can take place via command line interpreter (or shell) /terminal window.

Command cat – concatenate

                This command concatenate file or files and puts it in the standard output device.

e.g 1:     cat file1

                cat file1 file2 concatenate file1 and file2 and puts in standard output.

                Cat file1 file2 > file3 concatenate file1 and file2 and makes the file3.

Ls or directory command

                Lists files and sub-directories in directory

                                ls – contents of directory

                                ls filename

                                ls directory (lists contents of directory)

                                ls –a list all files including hidden one

                                ls – al detail list of contents

                                ls –F marks directories with / and executable files as *

                                ls *.doc list all files with extention doc

                                ls –lt list with time of last modification

                                ls –lut show time of last time access

more command

                one screen at a time

                                some helpful tips using more command is

                                                h for help

                                                space for page

                                                b for back

                                                q for quit

                                                /string to search string

                E.g  cat file1.c|more

cp command

                cp command used to copy files. This over writes a file until unless specified.

                Syntax : cp [options]  <source file/s> <destination directory/file>\

               

Options	function
-i	Promotes before overwriting
-r	Copies entire directory

cp f1 f2 copies f1 to f2

cp  *.text dir copies all files with extention .text to directory dir

cp f1 f2 f3 f4 here f4 is taken as destination f1,f2,f3 as source

cp f1 dir copies file f1 to dir directory

cmp command

                cmp command used to compare two files and find is that files identical

                syntax:

                                cmp [options] file1 file2

                                E.g:         cmp jc.txt jaya.txt

                                                cmp –l jc.txt jaya.txt

mv command

                move command mv moves file(s) to specified directory/file. To do this destination should have permission.

                mv file1 file2

                mv *.txt dir moves all files with extension .txt to dir directory

rm command

                 removes or deletes files or folders if permission allowed.

                rm file1 removes file

                rm ja?.txt deletes all text files with first two char ja and last four char .txt

                rm –i * deletes all files in the current directory but asks for each file before deleting

                rm –r/dir recursively delete all files including the directory

date,cal command

                date displays the date and time

                cal displays the current month calendar

                cal 2012 displays the calendar 2012

                cal march 2012 displays march calendar of 2012

                the above can also be given as cal 3 2012

who command

                shows all the user who have logged in

                                with login name,terminal type and number,date and time (* note this info is displayed to users those who r not logged in from the server)

                whoami – displays self user name

                who –q who without detail.

Command finger

                This utility used to get list of user names,full name,terminal name,write status,idle time,login time,machine address.

Word count command

                wc filename list the number of lines,words,char from a file

head command

                Displays first n lines of a file

Tail command

                Displays last n lines of a file

Uname command

                Displays the name of the current system

                Uname [-a] [-i] [-m] [-p][-r] [-s] [-v][-x][-s systemname]

Clear

                To clear the screen

File

                Determines the type of file

Which

                Determines where is the executable for file for the given program

                E.g – which perl , which java

Whereis

                Locates binary,source and manual page files for a command

                Syntax : whereis [-bmsu][-BMS directory] file name

                -b  searches only for binaries

                -m  searches only manual sections

                -s searches only for sources

Directory Related commands

                Pwd – current working directory

                Mkdir – make directory

                Rmdir – remove directory

Redirection and piping

                Redirection – redirecting a command result to a file

                Piping – result of one command is sent as input for another command

Redirection operators

Ø  Indicates redirection of out put., send the output of a command to a file or printer.,

>> indicates redirection of out put of a command to a file which will be appended at last.

Unix wont show the out put in screen/std out put but redicted to a file

E.g

                Cat >file

                Cat file>file1

                Cat file>>file1

<  Indicates redirection of in put., takes the input from a file for a command rather than keybord.,

E.g

                Cat<file

Piping Example

                $ls |wc –l

                                Output of ls is given as output of wc command.

                Pipe with redirection

                                $ls|wc –l>countfile

                $who|sort

                $who|sort>sorted

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