Linux Terminal: Seeing the unseen characters with cat!

Sometimes a program or software don’t start for a syntax error, and if you check the files there is nothing wrong..apparently.
There are a lot of characters that usually are not printed if you use a normal text editor, but you can easily check if they are present with your terminal and the command cat.

As first thing let’s create a simple text file with these special characters, open a terminal and run the command:

printf 'testing\012\011\011testing\014\010\012more testing\012\011\000\013\000even more testing\012\011\011\011\012' > /tmp/testing.txt

Now if you open the file with an editor you’ll have different results.
A simple cat will show:

$ cat /tmp/testing.txt 
testing
		testing
 
more testing
 
        even more testing

While if you open it with nano or vim you’ll see :

testing
                testing^L^H
more testing
        ^@^K^@even more testing

Now we can see some options of cat to print special characters.

1) Use cat -T to display TAB characters as ^I

cat -T /tmp/testing.txt
testing
^I^Itesting
 
more testing
^I
  even more testing
^I^I^I

2) Use cat -E to display $ at end of each line

$ cat -E /tmp/testing.txt
testing$
		testing
                      $
more testing$
 
        even more testing$
			$

3) Use a simple cat -A to show up all the invisible characters:

$ cat -A /tmp/testing.txt
testing$
^I^Itesting^L^H$
more testing$
^I^@^K^@even more testing$
^I^I^I$

Original article : http://linuxwiki.net/2013/07/30/cat-ile-gorunmeyen-karakterleri-gormek/

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