How can I reverse the order of lines in a file

Question

I d like to reverse the order of lines in a text file  or stdin   preserving the contents of each line   So  i e   starting with   foo bar baz   I d like to end up with   baz bar foo   Is there a standard UNIX commandline utility for this

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The simplest method is using the tac command  tac is cat s inverse  Example     cat order txt roger shah  armin van buuren fpga vhdl arduino c   java gridgain   tac order txt  gt  inverted file txt   cat inverted file txt fpga vhdl arduino c   java gridgain armin van buuren roger shah

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I had the same question  but I also wanted the first line  header  to stay on top  So I needed to use the power of awk  cat dax-weekly csv   awk  1   last   NR  line last     0    END   print line 1   for  i   last  i  gt  1  i--    print line i          PS also works in cygwin or gitbash

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It happens to me that I want to get the last n lines of a very large text file efficiently   The first thing I tried is tail -n 10000000 file txt  gt  ans txt  but I found it very slow  for tail has to seek to the location and then moves back to print the results   When I realize it  I switch to another solution  tac file txt   head -n 10000000  gt  ans txt  This time  the seek position just needs to move from the end to the desired location and it saves 50  time   Take home message   Use tac file txt   head -n n if your tail does not have the -r option

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For Emacs users  C-x h  select the whole file  and then M-x reverse-region  Also works for only selecting parts or the lines and reverting those

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You can do it with vim stdin and stdout  You can also use ex to be POSIX compliant  vim is just the visual mode for ex  In fact  you can use ex with vim -e or vim -E  improved ex mode   vim is useful because unlike tools like sed it buffers the file for editing  while sed is used for streams  You might be able to use awk  but you would have to manually buffer everything in a variable   The idea is to do the following    Read from stdin For each line move it to line 1  to reverse   Command is g   m0  This means globally  for each line g  match the start of the line  which matches anything    move it after address 0  which is line 1 m0  Print everything  Command is  p  This means for the range of all lines    print the line p  Forcefully quit without saving the file  Command is q   This means quit q  forcefully          Generate a newline delimited sequence of 1 to 10   seq 10 1 2 3 4 5 6 7 8 9 10    Use - to read from stdin    vim has a delay and annoying  Vim  Reading from stdin     output   if you use - to read from stdin  Use --not-a-term to hide output    --not-a-term requires vim 8 0 1308  Nov 2017    Use -E for improved ex mode  -e would work here too since I m not   using any improved ex mode features    each of the commands I explained above are specified with a   sign   and are run sequentially    seq 10   vim - --not-a-term -Es   g   m0     p    q   10 9 8 7 6 5 4 3 2 1   non improved ex mode works here too  -e    seq 10   vim - --not-a-term -es   g   m0     p    q      If you don t have --not-a-term  use  dev stdin seq 10   vim -E   g   m0     p    q    dev stdin    POSIX compliant  maybe    POSIX compliant ex doesn t allow using   sign to specify commands    It also might not allow running multiple commands sequentially    The docs say  Implementations may support more than a single -c    If yours does support multiple -c   seq 10   ex -c  execute -c  g   m0  -c   p  -c  q    dev stdin    If not  you can chain them with the bar     This is same as shell   piping  It s more like shell semi-colon       The g command consumes the    so you can use execute to prevent that    Not sure if execute and   is POSIX compliant  seq 10   ex -c  execute  g   m0     p   q    dev stdin     How to make this reusable  I use a script I call ved  vim editor like sed  to use vim to edit stdin  Add this to a file called ved in your path      usr bin env sh  vim - --not-a-term -Es         p   q     I am using one   command instead of    p    q    because vim limits you to 10 commands  So merging them allows the      to have 9   commands instead of 8   Then you can do   seq 10   ved   g   m0    If you don t have vim 8  put this in ved instead      usr bin env sh  vim -E         p   q    dev stdin

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rev text here   or  rev  lt file gt    or  rev texthere

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This will work on both BSD and GNU   awk   arr i     0  END  while  i gt 0  print arr --i     filename

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Just Bash     4 0    function print reversed       local lines i     readarray -t lines      for    i      lines      i--      do         printf   s n     lines i        done    print reversed  lt  file

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Best solution   tail -n20 file txt   tac

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sort -r  lt  filename   or  rev  lt  filename

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BSD tail   tail -r myfile txt   Reference  FreeBSD  NetBSD  OpenBSD and OS X manual pages

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tail -r works in most Linux and MacOS systems  seq 1 20   tail -r

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There s the well-known sed tricks     reverse order of lines  emulates  tac     bug feature in HHsed v1 5 causes blank lines to be deleted sed  1 G h   d                  method 1 sed -n  1 G h  p                method 2    Explanation  prepend non-initial line to hold buffer  swap line and hold buffer  print out line at end   Alternatively  with faster execution  from the awk one-liners   awk   a i     0  END  for  j i-1  j gt  0   print a j--     file    If you can t remember that   perl -e  print reverse  lt  gt     On a system with GNU utilities  the other answers are simpler  but not all the world is GNU Linux

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If you happen to be in vim use   g   m0

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Also worth mentioning  tac  the  ahem  reverse of cat   Part of coreutils   Flipping one file into another  tac a txt  gt  b txt

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at the end of your command put    tac  tac does exactly what you re asking for  it  Write each FILE to standard output  last line first    tac is the opposite of cat  -

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If you want to modify the file in place  you can run sed -i  1 G h   d  filename  This removes the need to create a temporary file and then delete or rename the original and has the same result  For example   tac file  gt  file2  sed -i  1 G h   d  file  diff file file2    Based on the answer by ephemient  which did almost  but not quite  what I wanted

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tac 2 gt   dev null    tail -r    Try tac  which works on Linux  and if that doesn t work use tail -r  which works on BSD and OSX

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tac  lt file name gt    example     cat file1 txt 1 2 3 4 5    tac file1 txt 5 4 3 2 1

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EDIT the following generates a randomly sorted list of numbers from 1 to 10   seq 1 10   sort -R   tee  tmp lst  cat  lt  cat  tmp lst   lt  echo  -------             where dots are replaced with actual command which reverses the list  tac  seq 1 10   sort -R   tee  tmp lst  cat  lt  cat  tmp lst   lt  echo  -------      lt  tac    python  using    -1  on sys stdin  seq 1 10   sort -R   tee  tmp lst  cat  lt  cat  tmp lst   lt  echo  -------      lt  python -c  import sys  print    join   line for line in sys stdin     -1

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I see lots of interesting ideas  But try my idea  Pipe your text into this       rev   tr   n        rev   tr       n    which assumes that the character     is not in the file  This should work on every UNIX shell going back to 1961  Or something like that

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I really like the  tail -r  answer  but my favorite gawk answer is      gawk    L n       0      END   while n--           print L n     file

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You may use Perl on the commandline  perl -e  my  b     while  lt  gt    push  b         print join  quot  quot   reverse  b     orig  gt  rev

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For cross OS  i e  OSX  Linux  solution that may use tac inside a shell script use homebrew as others have mentioned above  then just alias tac like so   Install lib  For MacOS  brew install coreutils   For linux debian   sudo apt-get update sudo apt-get install coreutils    Then add alias  echo  alias tac  gtac    gt  gt     bash aliases  or wherever you load aliases  source    bash aliases tac myfile txt

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Try the following command   grep -n    myfile txt   sort -r -n   gawk -F      print  2

[shell] How can I reverse the order of lines in a file?

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