Well, as a general advice you should carefully read the man pages, especially when looking for options and their meaning. For example:
Code:
$ man cat
<scroll>
-n, --number
number all output lines
-s, --squeeze-blank
suppress repeated empty output lines
<omitted>
At this point some exercise is useful to test our understanding. For example I create a file with 4 lines (leaving two lines in the middle empty) using echo and redirection:
Code:
$ echo first line > file
$ echo >> file
$ echo >> file
$ echo fourth line >> file
Ok. Let's try with cat and its options:
Code:
$ cat file
first line
fourth line
The above is just the content of the file, as expected (a usage of cat - without options - is to print out the content of a file). Let's try our options:
Code:
$ cat -n file
1 first line
2
3
4 fourth line
$ cat -s file
first line
fourth line
Mirroring your question, what's the difference between -n and -s now?
