Filters in UNIX

   A filter is a UNIX command which which will extract(select) some data from a given text file. The following are some of the filters available in UNIX

i)uniq ii) grep  iii)cut  iv) paste  v) join  vi)

i) uniq command:

     This command line displays unique lines from the given file i.e., if two successive lines are same in a file then duplicate lines will be removed.

/netsem2014/anil/~ cat>sample.txt
hi how are you
hi where are you
hi where are you
bye take care.

/netsem2014/anil/~ uniq -c sample.txt
hi how are you
hi where are you
bye take care.

grep command:

          This command is used to select lines from a file having some specified string.

   /nesem2014/anil/~ cat>sample.txt

  hi how are you?
  who are you?
  welcome here.
  bye take care.

 /netsem2014/anil/~ grep "are" sample.txt
(the above command combination displays the lines containing are)

 hi how are you?
 who are you?



/netsem2014/anil/~ grep "^who" sample.txt
(the above command combination displays the lines which starts with string hi)

hi how are you?



/netsem2014/anil/~ grep "you$" sample.txt
(the above command combination displays the lines which ends with you)

hi how are you?
who are you?

/netsem2014/anil/~ grep -n "hi" sample.txt
(the above command combination displays those lines having string hi along with their line numbers)

/netsem2014/anil/~ grep -v "hi" sample.txt
(the above command combination displays those lines that not containing hi)

welcome here
bye tc

cut command:
     This command is used to cut some words from the given line or file.

  /netsem2014/anil/~ cat>sample.txt
   hi how are you
   UNIX is a multi user operating system
   bye take care.

  /netsem2014/anil/~ cut -f1,2 sample.txt
  (the above command combination displays first and second word of each file in a given file)

  hi how
 UNIX is
 bye take

/netsem2014/anil/~ cut -c 4 sample.txt
(the above command combination displays fourth character of each line in a given file)

 h
 X

paste command:

   This command is used to join the files vertically

   /netsem2014/anil/~ cat>sample1.txt
   hi how are you?
  /netsem2014/anil/~ cat>sample2.txt
  where are you?

 /netsem2014/anil/~ paste sample1 sample2>sample3

/netsem2104/anil/~ cat>sample3
 hi how are you?
 where are you?



filters in linux, cut command, paste command, join command,awk,sed command, grep command, egrep, fgrep,