BASIC UNIX COMMANDS,CONTROL STRUCTURES & LOOPS

UNIX COMMANDS :-

·        ‘who’ – To  list a number of users who logged in the system.

·        ‘who am  I’ – To know your id.

·        Cat>filename – To create an file

·        $clear – To clear the screen.

·        $cp__ – copies the file to (filename1-source file,filename2-destination file)

·        $mv__ – to rename the file< filename1> to

·        $rm_ – to remove the file

·        $rm_-i- – to remove the file but in interactively user friendly manner

LISTING OF FILES :-

·        Wild card characters: ‘?’ replaces 1 character

·        ‘*’ – replaces none, one or more characters

·        ‘[]’- or  [ abc ] – replaces or lists filename beginning with a or b or c.

·        $ls – lists the file

·        $ls_-a – lists the file including hidden files

·        $ls_??? – lists filename which has 3 characters

·        $ls_a?a – lists filename which has 3 characters and second character must be (a)

·        $ls_a* - lists filename beginning with (a) ex: a,a1,a12...... 

·        $ls_*a* - it can end and begin with any character but the middle character must be a

·        $ls_[abc]* - it starts with a or b or c followed by ‘n’ number of characters

·        $ls_[!aeiou]* - lists file name which does not begin with a vowel (! = should not)

MORE COMMANDS :-

·        $cal – to display the calendar

·        $cal – 2 2010 [February 2010]

·        $date – display the login name of the user

·        $uname – display name of the system

·        $vname – display additional information

·        $tty – display name of the terminal

·        $wc_lwc - counts the number of words/characters of a given file

·        $wc_-lc - displays only characters and lines

·        $file_* - displays the type of files

·        $pid – processes which is running

·        $mk dir

·        $rm

·        $cd.. - goes one level higher

·        $cd/ - to go to root directory

·        $cd – to go to home directory

·        $rm_-r - to remove the contents of directory and directory itself at one short

·        $mv - to move the contents of filename1 to filename2

·        $pg - to see the contents pagewise

·        $head_-10 - to see the first 10 lines of the file

·        $tail_-10   – to see the last 10 lines of the file

·        $mkdir –p - to make the folder at one go

·        $rmdir –p - to remove the folder

·        $file * - to display al types of file

·        $cat - to display the contents of more than one file at a time

·        $cat >> - to append filename1 to filename2

·        $cat >> - to append two files to one file

	FILTER	PURPOSE
1.	cat	Concatenates and displays files
2.	pg	Paginates display for terminals
3.	more	Displays a file one screen-full at a time
4.	head	Prints the first few lies of a file
5.	tail	Displays the last few lines of a file
6.	grep	Searches files for a pattern
7.	sort	Sorts and merges files
8.	wc	Counts number of lines, words and characters in a file
9.	uniq	Reports unique lines in a file
10.	tr	Translates characters in a file
11.	cut	Cuts out selected columns and fields of a file
12.	paste	Merges lines of files (horizontal merging)
13.	nl	Adds line numbers to a file
14.	pr	Prints files to standard output
15	lpr	Sends requests to line printer

	SORT FILTER
	OPTIONS	MEANING
1.	-b	Ignores leading spaces and tabs
2.	-c	Checks if files are already sorted. If they are, sort does nothing
3.	-d	Sorts in dictionary order
4.	-f	Ignores case
5.	-m	Merges files that have already been sorted
6.	-n	Sorts in numeric order
7.	-o file	Stores output in file The default is to send output to standard output
8.	-r	Reverses sort
9.	-tc	Separates fields with delimitor character (default tab)
10.	-u	Unique output
11.	+n -m	Skips n fields before sorting and then sorts on field m

	GREP FILTER
	OPTIONS	MEANING
1.	-c	Returns only the number of matches, without quoting the text (count)
2.	-i	Ignores case while searchin
3.	-l	Returns only filenames containing a match without quoting the text
4.	-n	Returns line numbers of matched texts as well as the text itself
5.	-s	Suppresses error messages
6.	-v	Returns lines that do not match the text

	RELATIONAL OPERATORS
1.	>	-gt
2.	<	-lt
3.	>=	-ge
4.	<=	-le
5.	==	-eq
6.	!=	-ne
	LOGICAL OPERATORS
1.	and	-a
2.	or	-o
3.	not	!
	ARITHMETIC OPERATORS
1.	Addition	+
2.	Subtraction	-
3.	Multiplication	\*
4.	Division	/
5.	Modulus	%

Writing a unix shellscript program:-

·        $vi .sh – to create a unix file

·        ‘echo’ – to print the statements/output on the screen

·        ‘read’ – to take the contents/inputs from the keyboard

·        :wq! – to save the file

·        $sh - to run shellscript program

·        bc – best calculator

·        # - to insert comments

FORMS OF IF STATEMENT

 If

Syntax:

   if [ control command ]

   then

     Statement1

   fi

If else

Syntax:

   if [ control command ]

   then

     Statement1

   else

     Statement2

   fi

If else ladder    

Syntax:

   if [ control command 1 ]

   then

     Statement1

   else

   if [ control command 2 ]

   then

     Statement2

   else

     Statement3

   fi

   fi 

NESTED IF

Syntax:

   if [ control command 1 ]

   then

     Statement1

     if [ control command 2 ]

     then

       Statement2

     else

     Statement3

   fi

  else

   fi 

ELIF STRUCTURE

Syntax:

   if [ control command 1 ]

   then

     Statement1

   elif [ control command 2 ]

     then

       Statement2

   elif [ control command 3 ]

     then

       Statement3

  else

       Statement4

   fi

CASE CONTROL STRUCTURES

Until statement

Syntax:

   until [ control statement ]

   do

      Statement 1

      Statement 2 …

      Statement N

   done

For Loop

Syntax:

1. for ((initialization, condition, update))

   do

      Statement 1

      Statement 2 …

      Statement N

    done

2. for control-variable n value1 value2 value3

   do

      Statement 1

      Statement 2 …

      Statement N

   done

CASE ESAC CONTROL STRUCTURES

Case value in

    1)

       do this

       and this

       ;;

    2)

       do this

       and this

       ;;

    3)

       do this

       and this

       ;;

    *)

       do this

       ;;

  esac