How can I delete a newline if it is the last character in a file

Question

I have some files that I d like to delete the last newline if it is the last character in a file   od -c shows me that the command I run does write the file with a trailing new line   0013600   n   t   gt    n   I ve tried a few tricks with sed but the best I could think of isn t doing the trick   sed -e   s        n   1   abc   Any ideas how to do this

User · Answer

You can take advantage of the fact that shell command substitutions remove trailing newline characters:

Simple form that works in bash, ksh, zsh:

printf %s "$(< in.txt)" > out.txt

Portable (POSIX-compliant) alternative (slightly less efficient):

printf %s "$(cat in.txt)" > out.txt

Note:

If in.txt ends with multiple newline characters, the command substitution removes all of them.^{Thanks, Sparhawk} (It doesn't remove whitespace characters other than trailing newlines.)
Since this approach reads the entire input file into memory, it is only advisable for smaller files.
printf %s ensures that no newline is appended to the output (it is the POSIX-compliant alternative to the nonstandard echo -n; see http://pubs.opengroup.org/onlinepubs/009696799/utilities/echo.html and https://unix.stackexchange.com/a/65819)

A guide to the other answers:

If Perl is available, go for the accepted answer - it is simple and memory-efficient (doesn't read the whole input file at once).
Otherwise, consider ghostdog74's Awk answer - it's obscure, but also memory-efficient; a more readable equivalent (POSIX-compliant) is:
awk 'NR > 1 { print prev } { prev=$0 } END { ORS=""; print }' in.txt
Printing is delayed by one line so that the final line can be handled in the END block, where it is printed without a trailing \n due to setting the output-record separator (OFS) to an empty string.
If you want a verbose, but fast and robust solution that truly edits in-place (as opposed to creating a temp. file that then replaces the original), consider jrockway's Perl script.

User · Answer

I had a similar problem  but was working with a windows file and need to keep those CRLF -- my solution on linux   sed  s  r  g  orig   awk   if  NR gt 1  printf   r n    printf   s   0     gt  tweaked

User · Answer

ruby   ruby -ne  print  stdin eof      strip         or   ruby -ane  q p p    puts q if    gt 1 END print p strip

User · Answer

A fast solution is using the gnu utility truncate     -z   tail -c1 file     amp  amp  truncate -s-1 file   The test will be true if the file does have a trailing new line   The removal is very fast  truly in place  no new file is needed and the search is also reading from the end just one byte  tail -c1

User · Answer

Here is a nice  tidy Python solution   I made no attempt to be terse here   This modifies the file in-place  rather than making a copy of the file and stripping the newline from the last line of the copy   If the file is large  this will be much faster than the Perl solution that was chosen as the best answer   It truncates a file by two bytes if the last two bytes are CR LF  or by one byte if the last byte is LF   It does not attempt to modify the file if the last byte s  are not  CR LF   It handles errors   Tested in Python 2 6   Put this in a file called  striplast  and chmod  x striplast      usr bin python    strip newline from last line of a file   import sys  def trunc filename  new len       try            open with mode  append  so we have permission to modify           cannot open with mode  write  because that clobbers the file          f   open filename   ab           f truncate new len          f close       except IOError          print  cannot write to file    filename         sys exit 2     get input argument if len sys argv     2      filename   sys argv 1  else      filename    --help     wrong number of arguments so print help  if filename     --help  or filename     -h  or filename              print  Usage   s  lt filename gt     sys argv 0      print  Strips a newline off the last line of a file       sys exit 1    try        must have mode  b   binary  to allow f seek   with negative offset     f   open filename   rb   except IOError      print  file does not exist    filename     sys exit 2    SEEK EOF   2 f seek -2  SEEK EOF     seek to two bytes before end of file  end pos   f tell    line   f read   f close    if line endswith   r n        trunc filename  end pos  elif line endswith   n        trunc filename  end pos   1    P S  In the spirit of  Perl golf   here s my shortest Python solution   It slurps the whole file from standard input into memory  strips all newlines off the end  and writes the result to standard output   Not as terse as the Perl  you just can t beat Perl for little tricky fast stuff like this   Remove the   n  from the call to  rstrip   and it will strip all white space from the end of the file  including multiple blank lines   Put this into  slurp and chomp py  and then run python slurp and chomp py  lt  inputfile  gt  outputfile   import sys  sys stdout write sys stdin read   rstrip   n

User · Answer

perl -pe  chomp if eof  filename  gt filename2   or  to edit the file in place   perl -pi -e  chomp if eof  filename    Editor s note  -pi -e was originally -pie  but  as noted by several commenters and explained by  hvd  the latter doesn t work    This was described as a  perl blasphemy  on the awk website I saw   But  in a test  it worked

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If you want to do it right  you need something like this   use autodie qw open sysseek sysread truncate    my  file   shift  open my  fh     gt  gt     file  my  pos   tell  fh  sysseek  fh   pos - 1  0  sysread  fh  my  buf  1 or die  No data to read     if  buf eq   n        truncate  fh   pos - 1      We open the file for reading and appending  opening for appending means that we are already seeked to the end of the file   We then get the numerical position of the end of the file with tell   We use that number to seek back one character  and then we read that one character   If it s a newline  we truncate the file to the character before that newline  otherwise  we do nothing   This runs in constant time and constant space for any input  and doesn t require any more disk space  either

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This is a good solution if you need it to work with pipes redirection instead of reading output from or to a file  This works with single or multiple lines  It works whether there is a trailing newline or not     with trailing newline echo -en  foo nbar n    sed   s        head -c -1    still works without trailing newline echo -en  foo nbar    sed   s        head -c -1    read from a file sed   s      myfile txt   head -c -1   Details    head -c -1 truncates the last character of the string  regardless of what the character is  So if the string does not end with a newline  then you would be losing a character  So to address that problem  we add another command that will add a trailing newline if there isn t one  sed   s        The first   means only apply the command to the last line  s     means substitute the  end of the line  with  nothing   which is basically doing nothing  But it has a side effect of adding a trailing newline is there isn t one    Note  Mac s default head does not support the -c option  You can do brew install coreutils and use ghead instead

User · Answer

gawk     awk   q p p  0 NR gt 1 print q END ORS       print p   file

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POSIX SED          d      - match last line     COMMANDS   - A group of commands may be enclosed between   and   characters  This is particularly useful when you want a group of commands to be triggered by a single address  or address-range  match

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sed -n  1 x 1  H    x s  n    p     YourFile   Should remove any last occurence of  n in file  Not working on huge file  due to sed buffer limitation

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Yet another answer FTR  and my favourite    echo cat the thing you want to strip and capture the output through backticks  The final newline will be stripped  For example     Sadly  outputs newline  and we have to feed the newline to sed to be portable echo thingy   sed -e  s thing sill      No newline  Happy  out  echo thingy   sed -e  s thing sill    printf  s   out     Similarly for files  file  cat file ending in newline  printf  s   file   gt  file no newline

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Assuming Unix file type and you only want the last newline this works   sed -e        d     It will not work on multiple newlines       Works only if the last line is a blank line

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Using dd   file   path to file        tail -c 1    file     tr -dc   n    wc -c   -eq 1     amp  amp        printf      dd  of    file   seek      stat -f   z     file    - 1   bs 1 count 1      printf      dd  of    file   seek      wc -c  lt     file    - 1   bs 1 count 1

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A very simple method for single-line files  requiring GNU echo from coreutils    bin echo -n   cat  file

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head -n -1 abc  gt  newfile tail -n 1 abc   tr -d   n   gt  gt  newfile    Edit 2    Here is an awk version  corrected  that doesn t accumulate a potentially huge array       awk   if  line  print line  line  0  END  printf  0   abc

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perl -pi -e  s  n    if eof   your file

User · Answer

perl -e  local           lt    s  n     print  a-text-file txt   See also Match any character  including newlines  in sed

User · Answer

sed   a    n     d N     n  ba  file

User · Answer

Yet another perl WTDI   perl -i -p0777we s  n z    filename

User · Answer

The only time I ve wanted to do this is for code golf  and then I ve just copied my code out of the file and pasted it into an echo -n  content  gt file statement

User · Answer

You can do this with head from GNU coreutils  it supports arguments that are relative to the end of the file  So to leave off the last byte use   head -c -1   To test for an ending newline you can use tail and wc  The following example saves the result to a temporary file and subsequently overwrites the original   if      tail -c1 file   wc -l     1     then   head -c -1 file  gt  file tmp   mv file tmp file fi   You could also use sponge from moreutils to do  in-place  editing        tail -c1 file   wc -l     1     amp  amp  head -c -1 file   sponge file     You can also make a general reusable function by stuffing this in your  bashrc file     Example   remove-last-newline  lt  multiline txt function remove-last-newline        local file   mktemp      cat  gt   file     if      tail -c1  file   wc -l     1     then         head -c -1  file  gt   file tmp         mv  file tmp  file     fi     cat  file     Update  As noted by KarlWilbur in the comments and used in Sorentar s answer  truncate --size -1 can replace head -c-1 and supports in-place editing

[linux] How can I delete a newline if it is the last character in a file?

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