0

Given a data file tmp_file,

5 0 0 0
0 5 0 0
0 0 6 0
0 0 0 6

the following two commands render different results, why is that?

sed 's/\n/ /g' tmp_file
5 0 0 0
0 5 0 0
0 0 6 0
0 0 0 6

sed 's/0/ /g' tmp_file  
5      
  5    
    6  
      6

EDIT:

a previous post, How can I replace a newline (\n) using sed?, was suggested to have resolved the issue. Surely the solution is the same, but the question looks seemingly different in the eye of a newbie. Also, one should not expect anybody is able to find the right answer among millions of posts even with hours of research online as done in the current post. I would rather withdraw the post if a negative mark is given due to being similar to previous posts.

bsmile
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  • Possible duplicate of [How can I replace a newline (\n) using sed?](https://stackoverflow.com/questions/1251999/how-can-i-replace-a-newline-n-using-sed) – Wiktor Stribiżew Nov 18 '18 at 11:59
  • See [here](https://www.gnu.org/software/sed/manual/sed.html#Execution-Cycle) for how the sed cycle is defined. – potong Nov 19 '18 at 11:45

1 Answers1

1

Let us try to understand how sed reads the Input_file, so sed reads the lines by separator which is new line it self. Which means if lines are separated with new line a single line CANNOT have new line in it, until/unless we do let sed know to read whole Input_file in a loop and then replace the new lines(kind of keeping values in hold space which is out of box functionality provided by sed to keep values save in memory for operational purposes). So that is why your first command is NOT having any affect since sed not found any line which is having new line in it.

Here is very nice thread(How can I replace a newline (\n) using sed? ) I found over SO you could go through its solution and its explanation(taken from that thread) as follows.

sed ':a;N;$!ba;s/\n/ /g' Input_file

Explanation of above code:

1-Create a label via :a.

2- Append the current and next line to the pattern space via N.

3- If we are before the last line, branch to the created label $!ba ($! means not to do it on the last line as there should be one final newline).

4- Finally the substitution replaces every newline with a space on the pattern space (which is the whole file).

I wanted to add my explanation above and then add that thread's details.

RavinderSingh13
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  • Thank you very much for the explanation. Now I get it! So indeed \n and other character(regular or special) are different. Basically, you said that I need to read in the whole input file in order to do the replacement of \n with space. BTW, N might refer to only append the next line to the pattern buffer instead of including the current line as well, or otherwise, every time the process branches, the current line would be read in twice. Is it? – bsmile Nov 18 '18 at 03:30