Linux filter commands,Lessons2All

Linux: Filter commands cut, wc, spell and sort

The cut linux filter command cuts off and picks up a given number of character or fields from the specified file
For example if you want to display only selected fields from the database of students say name and class then you can use cut command.
In the following example user displays the values of the fields name and class which is the 2nd and 4th field respectively in the database studentinfo

Example: cut –f 2, 4 studentinfo

If we want to view through few fields, for example 1 through 4 then we can use the following command

Example: cut –f 1-4 studentinfo

The cut command assumes that the fields are separated by a tab character. If the fields are delimited by some character other than the default tab character, cut supports an option ‘–d’ which allows us to set the delimiter

For example the file studentinfo may have the information for each student stored in the following format

Example: Rollnum:Name:age:Class:Adrress:City:Pin: Country

Each piece of information is separated by a colon, hence we require the field delimiter to be recognized as ‘:’.The command for listing the name and the class field is now will be cut –f 2,4 –d “:” studentinfo
The cut command can also cut specified columns from a file and display them on the standard output.The switch used for this purpose is ‘–c’

Example: cut –c 1-7 studentinfo

The linux command wc filter takes data stream as its input, which is usually data read from a file. It then counts the number of lines, words, and characters (including the newline character, found at the end of a line) in the file and outputs these counts
In the following example given, the wc command is used to find the number of lines, words, and characters in the file named as karan

Example: wc karan

The linux command spell filter checks the spelling of words in its input and outputs only the misspelled words
In the following example the command checks for the spelling of the words in the file karan and displays the misspelled words

Example: spell karan

Now using redirection, you can save those words in a file
With a pipe, you can also print them
In the next example, the user saves the misspelled words to a file called wrongspell

Example: spell karan > wrongspell

You can pipe the output of one filter into another filter, in effect, applying the capabilities of several filters to your data

For example, suppose you only want to know the number of words that are misspelled
You could pipe the output of the spell filter into the wc filter, which would count the number of misspelled words

In the next example, the words in the karan file are checked for its spelling, and the list of misspelled words is piped to the wc filter. The wc filter, with its -w option, then counts those words and outputs the count

Example: spell karan | wc -w

The linux sort filter outputs a sorted version of a file
Sort is a useful utility with many different sorting options. These options are primarily designed to operate on files arranged in a database format
The sort filter sorts, character by character, on a line
If the first character in two lines is the same, sort will sort on the next character in each line
You can, also save the sorted version in a file or send it to the printer
In the following example, the user saves the sorted output from the file karan in a file called raj

Example: sort karan > raj