Unix Fundamentals

In this session, you learn about:

•          The functions of OS

•          The history of Unix

•          The features of UNIX

•          The Unix architecture

•          Process management

•          File management

Operating System (OS)

•          OS is a system software

•          OS can be defined as an organized collection of software consisting of procedures for operating a computer

•          OS provides an environment for execution of programs

•          OS acts as an interface between the user and the hardware of the computer system.

•          Operating system interacts with user in two ways

•          Operating system commands

                               Enables user to interact directly with the operating system.

•          Operating system calls

                               Provides an interface to a running program and the operating system. System calls in UNIX are written in C.

History of UNIX

•          Ken Thompson of AT&T Bell Laboratories designed UNIX in late 1960s

•          Two versions of UNIX that emerged are AT&T Unix and BSD Unix

•          In 1989, AT&T and Sun Microsystems joined together and developed system V release 4 (SVR4)

•          Two of the main standards mainly in use are POSIX (Portable Operating System Interface) and  X/open standard. In 1988, MIT formed Xconsortium developed vendor-neutral Xwindow System.

Features of UNIX

•          UNIX is multi tasking and multi user operating system

•          UNIX is a character user interface (CUI ) operating system

•          UNIX is a open source operating system

•          Portability – Can we use it on any OS

•          Modularity – Can change the source code

•          File structure

•          Security

•          Strong networking support & advanced graphics

Layered Architecture

Shell

•          Acts as an interface between user and kernel

•          User commands will be interprets and carried out to kernel.

•          Its features include control flow primitives, parameter passing, variables and string substitution.

Kernel

•          Kernel will act as a interface between shell and hardware components.

•          Core of the operating system

•          Collection of system calls mostly written in C language

•          Interacts directly with the hardware

•          Allocates time and memory to programs and facilities IPC’s

•          Helps in I/O services.

Standard directories in UNIX

                                                                                                                                                                            

•          /etc             stores the system administration utility files

•          /bin             stores the most commonly used unix commands

•          /usr              stores all user home directories and some Unix commands

•          /dev             stores all device files

•          /lib                stores library files for C programming

•          /tmp             used for temporary storage

File access permissions

•          A- total number of disk blocks occupied by the files

•          B- type of the file

–        - ordinary file

–        d – directory

–        c- character device

–        b – block device

•          C- its access permissions

•          D- number of links to the file

•          E- the owner of the file

•          F- the group of the owner of the file

•          G- the size of the file in bytes

•          H- the date and time of last modification

•          I – the file name

Absolute mode

•          Based on octal numbers

–        No access                                                                                                                              0

–        Execute access only                                                                                                          1

–        Write access only                                                                                                               2

–        Read access only                                                                                                                4

–        Write and execute access                                                                                              2+1=    3

–        Read and execute                                                                                                            4+1=    5

•          $chmod 400 mydoc.doc                                                                                                                  

•          Exercise

•          Write the command to change the permission of the file mydoc.doc

–        Read and write for the owner

–        Write and execute for the group

–        Execute only for others ( both in symbolic and absolute)

cat command

•          Helps you to create a file

•          $ cat > filename

•          cat filename helps to view the contents of the file.

touch command

•                -- Will allow to create multiple 0 byte files

•                     $ touch file1 file2 file3

VI command

•                  $ vi <filename>

•                  If the file doesn’t exist, it will create otherwise open the existing one.

Creating a directory:

•          You can create a directory by using the mkdir command. For example, to create a directory named dir1 within the current working directory:

–        $ mkdir  dir1

–        $ mkdir /usr/user1/dir1

–        Options

            cd command

–        To change the directory to dir1 type

–        cd dir1

            pwd

–        To see the current working directory

Removing a directory

•          Removes a directory

•          To remove a directory

–        Must be empty

–        Should not be the current directory or at a higher level

–        Should not be the home directory

–        -p -> Removes all directories along the path name specified

–        $ rmdir  -p /home/demo/mydir

Removing files

•          To delete a file

                                                                            $ rm <file_name>

•          You can remove more than one file at a time.

                                                                           $ rm oldbills oldnotes oldjokes

            would remove the three named files.

                                                  Options

                                                              -r à recursive

                                                              -i à interactive mode

                                                              -f à forceful

Basic commands for file handling

•         ls command

–        Lists the contents of your current working directory

–        Few useful options with ls are:-

•         -l             list in long format

•         -a            all files including those which begin with dot

•         -I             list the inode number in the first column

•         -x             sorts in multi column output across the page

•         -C            displays file in columns

•         -R            recursively list all directories and  subdirectories

•         -F             indicates the type if files using symbols like   */=@|

•         -ld           long listing of files in a directory

File management utilities

•         cp             : copy a file

                               $cp <file1> <file2>

•         mv            : move / rename a file

                               $ mv  <file1> <file2>

                               $ mv   file1 file2

                               $ mv   dir1/f ile1 dir2/fil2

Wc

wc  word count

•         -c character count

•         -w word count

•         -l line count

•         $ wc employee

•         To count the number of files in a directory

 To count the number of users currently logged in

WC –l   file1

WC –c   file1

Wc –w   fil1

Tr

•         Translates the input into some other form

Eg:

•         Convert all lowercase to uppercase

–        tr “[a-z]” “[A-Z]” file1

FIND

•         find command

–        Helps to find a file in the specified directory

–        The syntax is find <path> -name <filename>

•         find . –name doc1.doc

•         find .  /tmp/project –name new_data

•         find /usr –type d –name backup

•          

File Comparisons

•         comm : displays common lines in the two files

•         cmp    : to compare two files

•         diff      : reports the difference between two files

•         uniq    : display the duplicate and unique lines of a file

comm.

Cmp

•         Compares two files

              $ cmp file1 file2

    Eg:

        document1                                            document2

        This is a document.                              This is a document.

         $cmp document1 document2

        document1 document2 differ: char 6, line 1

diff

•         Reports the difference between two files

                             $diff [options] [file1][file2]

                    -b ignore trailing blanks

                   -h used for files of unlimited length

Eg:

              file1                                                           file2

              cal                                                              cal

              cp                                                               cp

              crypt                                                          crypt

               z                                                               cut

$ diff file1 file2

                      4c4

                      <z

                      -----

                     >cut

Uniq

•         Displays the duplicate and unique line of a file

•         $ uniq [option..] <filename>

–        -u        display only the unique lines

–        -d        display only the duplicate lines

–        -c        display all lines each preceded by the count of the records.

Miscellaneous Sending and receiving mails

•         $ mail <login name >

mail neeraj

Subject : …. <ctrl+d>

Input/ output redirection

•         Input redirection

•         Output redirection

•         Standard error redirection

Input redirection

•         Changing the default input source

•         Input redirection operator ‘<‘

•         $ command <filename

•         After the execution the standard input is reassigned to the default device

•         Eg :

–         $ cat <emp.dat ( similar output will be displayed by cat emp.dat)

Output redirection

•         Changing the default destination of the output

•         The output redirection operator : ‘ >’

•         $ command > filename

•         After the execution the standard output is reassigned to the default device

•         Eg:

–        $ cat emp.dat > emp.out

–        $ date > todays_date

–        $ cat > file1

–        $ cat >> file2

–         

Standard error redirection

•         0 standard input

•         1 standard output

•         2 standard error

•         $ command 2 > err_file

•         Eg :

–        $ cat emp.dat > newemp  2 > emp_err

Pipes and filters

•         Pipes :Connects two or more commands

•         Filters : Unix command which takes its input from standard input processes or filters it and generates and output.

–        grep

–        sort

–        cut

–        paste

–        head

–        tail

–        wc

–        pg

–        More

–        tr

Filters: grep

•         grep – ( global search for regular expression and print)

•         grep is the standard file searching and selection utility

•         $ grep [options] “pattern” <filename>

•         Options :

–        -n : prints line numbers

–        -v: the reverse search criterion

–        -c: display only a count of matching patterns

•         grep “madhu” emp.dat

–        Display the line(s) containing the string madhu.

•         grep –n “anurag” emp.dat

–        Display the lines containing the string anurag preceded by the line number

•         grep –v “Madhu” emp.dat

–        Display the lines of the file excluding the lines contatining the string Madhu.

Sort

•         sort [options] [-o output file name] [file name]

•         options

–        d         letters, digits and blanks

–        n         sort on the numeric field

–        r         reverse sort

–        u         eliminate duplicate lines                                                          

–        t           filed separator

–        o          stores the output

cut

•         Retrieves selected fields from a file

•         $ cut [options] <filename>

•         Options

–        -c      selects characters specified by list

–        -f       selects fields specified by list

–        -d      field delimiter

•         $ cut –c4-9 employee

–        Display characters 4 to 9 from each record

•         $ cut –d " " –f2-4 employee

–        Display 2-4 fields

•         $ cut –f 4- employee

–        Display 4^th field onwards

Paste

•         Merges files horizontally.

•         $ paste <file1> <file2>

•         Options –d  delimiter

Head and tail

•         head employee will display first 10 lines

•         head -5 employee

•         tail employee last 10 lines from the employee

•         tail -7 employee

•         tail +10 employee display lines from 10^th till the end of the file.

Others

The Unix manual

•         Information on all the commands can be found in the on-line manual pages.

•         $man <command>

•         Shows the details (syntax and description) of the command

•         help, info

•         $            end of the current line

•         ^ or 0    beginning of the current line

•         W         beginning of the next word

•         W         same as w, but ignores the punctuation

•         B           back to the beginning of the current word

•         E           end of the current word

•         Moving the cursor over the paragraph

{   to the beginning of the current paragraph

}   to the end of the current paragraph

n{   nth paragraph above the current paragraph

n}   nth paragraph below the current paragraph

•         Moving the cursor over sentences

(   first character of the sentence

)  last character of the sentence

Screen movements

Ctrl+D      scrolls down half a window

Ctrl+U      scrolls up half window

Ctrl+B      moves to the previous window

Ctrl+F       moves to the next window                                                                         

•         What is the command to move the cursor to the right by five words?

Modifying text

r, R          replace character

cw           change current word

nc            wchange n words

cc             change current line

nc            cchange n lines

c$            changes remainder of the line

Cutting and pasting

Yy       yanks the current line and puts in the buffer

Nyy    yanks n lines

Yw      yanks a word

Nyw    yanks n words

y$        yanks remainder of the line

P, p     copy the contents of the current buffer

U         undo all changes to the current line

U         undo the last command