Question

This is a very basic concept, but something I have never been able to articulate that well. and I would like to try to spell it and see where I go wrong.

If I have to, how would I define a “newline character”. say if I create a new file in unix(or windows), then does the file store the “end of line” information by inserting a special character in the file called as “new line character”. If so, what is its ascii value? I remember that in C programs, I have checked for the read character against the value ‘\n’ . And why this confusing 2 characters to represent end of line characters..

bash$ cat states
California
Massachusetts
Arizona

Say, I want to insert one line space between the lines and want an output of the form:
Desired output:

California

Massachusetts

Arizona

bash$sed -e 's/\n/\n\n/g' states  does not work.

Why can’t I treat “new line character” here just as I would treat any other character and run something like above command. (I understand that one might say that this is a matter of syntax of sed, but could one please explain the intuition behind not allowing this, so that I can get rid of my confusion.

Similarly, inside the vim editor, I can not use :%s/\n/\n\n/g . Why so?

Do I need to further escape \n by using a backslash in sed and from within vim?.

Thanks,

Jagrati

Answer 1

From the sed man page:

Normally, sed cyclically copies a line of input, not including its terminating newline character, into a pattern space, (unless there is something left after a “D” function), applies all of the commands with addresses that select that pattern space, copies the pattern space to the standard output, appending a newline, and deletes the pattern space.

It’s operating on the line without the newline present, so the pattern you have there can’t ever match. You need to do something else – like match against $ (end-of-line) or ^ (start-of-line).

Here’s an example of something that worked for me:

$ cat > states
California
Massachusetts
Arizona
$ sed -e 's/$/\
> /' states
California

Massachusetts

Arizona

I typed a literal newline character after the \ in the sed line.