What is newline character -- n

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

User · Answer

sed can be put into multi-line search  amp  replace mode to match newline characters  n   To do so sed first has to read the entire file or string into the hold buffer   hold space   so that it then can treat the file or string contents as a single line in  pattern space     To replace a single newline portably  with respect to GNU and FreeBSD sed  you can use an escaped  real  newline     cf  http   austinmatzko com 2008 04 26 sed-multi-line-search-and-replace  echo  California Massachusetts Arizona     sed -n -e     if the first line copy the pattern to the hold buffer 1h   if not the first line then append the pattern to the hold buffer 1 H   if the last line then           copy from the hold to the pattern buffer g   double newlines s  n      g s       p       output   California     Massachusetts     Arizona     There is  however  a much more convenient was to achieve the same result   echo  California Massachusetts Arizona        sed G

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I think this post by Jeff Attwood addresses your question perfectly  It takes you through the differences between newlines on Dos  Mac and Unix  and then explains the history of CR  Carriage return  and LF  Line feed

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I see a lot of sed answers  but none for vim   To be fair  vim s treatment of newline characters is a little confusing   Search for  n but replace with  r   I recommend RTFM    help pattern in general and  help NL-used-for-Nul in particular   To do what you want with a  substitute command     s      r   although I think most people would use something like   g   put      for the same effect   Here is a way to find the answer for yourself   Run your file through xxd  which is part of the standard vim distribution      xxd   You get  0000000  4361 6c69 666f 726e 6961 0a4d 6173 7361  California Massa 0000010  6368 7573 6574 7473 0a41 7269 7a6f 6e61  chusetts Arizona 0000020  0a                                           This shows that 46 is the hex code for C  61 is the code for a  and so on   In particular  0a  decimal 10  is the code for  n   Just for kicks  try   set ff dos   before filtering through xxd   You will see 0d0a  CRLF  as the line terminator    help       help  g  help  put  help     help 23 4

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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  gt  states California Massachusetts Arizona   sed -e  s      gt     states California  Massachusetts  Arizona   I typed a literal newline character after the   in the sed line

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Escape characters are dependent on whatever system is interpreting them   n is interpreted as a newline character by many programming languages  but that doesn t necessarily hold true for the other utilities you mention  Even if they do treat  n as newline  there may be some other techniques to get them to behave how you want  You would have to consult their documentation  or see other answers here    For DOS Windows systems  the newline is actually two characters  Carriage Return  ASCII 13  AKA  r   followed by Line Feed  ASCII 10   On Unix systems  including Mac OSX  it s just Line Feed  On older Macs it was a single Carriage Return

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sed  s    n   states

User · Answer

NewLine   n  is 10  0xA  and CarriageReturn   r  is 13  0xD    Different operating systems picked different end of line representations for files   Windows uses CRLF   r n    Unix uses LF   n   Older Mac OS versions use CR   r   but OS X switched to the Unix character   Here is a relatively useful FAQ

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Try this     sed -e   s  n  n n g  states

[c] What is newline character -- '\n'

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