How to use sed to remove the last n lines of a file

Question

I want to remove some n lines from the end of a file  Can this be done using sed   For example  to remove lines from 2 to 4  I can use    sed  2 4d  file   But I don t know the line numbers   I can delete the last line using    sed  d file   but I want to know the way to remove n lines from the end  Please let me know how to do that using sed or some other method

User · Answer

I prefer this solution   head -  gcalctool -s   cat file   wc -l -N  file   where N is the number of lines to remove

User · Answer

Try the following command   n   line number tail -r file name   sed  1 nd    tail -r

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From the sed one-liners     delete the last 10 lines of a file sed -e  a -e   d N 2 10ba  -e  P D      method 1 sed -n -e  a -e  1 10  P N D   N ba     method 2   Seems to be what you are looing for

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To truncate very large files truly in-place we have truncate command  It doesn t know about lines  but tail   wc can convert lines to bytes   file bigone log lines 3 truncate -s -  tail - lines  file   wc -c   file   There is an obvious race condition if the file is written at the same time  In this case it may be better to use head - it counts bytes from the beginning of file  mind disk IO   so we will always truncate on line boundary  possibly more lines than expected if file is actively written     truncate -s   head -n - lines  file   wc -c   file   Handy one-liner if you fail login attempt putting password in place of username   truncate -s   head -n -5  var log secure   wc -c   var log secure

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Use sed  but let the shell do the math  with the goal being to use the d command by giving a range  to remove the last 23 lines    sed -i       wc -l  lt  file -22     d  file   To remove the last 3 lines  from inside out     wc -l  lt  file    Gives the number of lines of the file  say 2196  We want to remove the last 23 lines  so for left side or range      2196-22     Gives  2174 Thus the original sed after shell interpretation is   sed -i  2174  d  file   With -i doing inplace edit  file is now 2173 lines   If you want to save it into a new file  the code is   sed -i  2174  d  file  gt  outputfile

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It can be done in 3 steps   a  Count the number of lines in the file you want to edit    n  cat myfile  wc -l    b  Subtract from that number the number of lines to delete    x    n-3     c  Tell sed to delete from that line number   x  to the end    sed   x   d  myfile

User · Answer

You could use head for this   Use     head --lines -N file  gt  new file  where N is the number of lines you want to remove from the file   The contents of the original file minus the last N lines are now in new file

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This will remove the last 12 lines  sed -n -e  a -e  1 10  P N D   N ba

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sed -n   pre 1 4  N b pre        cycle    P N D b cycle      YourFile   posix version

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With the answers here you d have already learnt that sed is not the best tool for this application     However I do think there is a way to do this in using sed  the idea is to append N lines to hold space untill you are able read without hitting EOF   When EOF is hit  print the contents of hold space and quit   sed -e     N N N N N N H    -e x   The sed command above will omit last 5 lines

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This might work for you  GNU sed    sed   a   N 1 4ba P  d D  file

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A funny  amp  simple sed and tac solution    n 4 tac file txt   sed  1  n d     tac   NOTE   double quotes   are needed for the shell to evaluate the  n variable in sed command  In single quotes  no interpolate will be performed  tac is a cat reversed  see man 1 tac the    in sed are there to separate  n  amp  d  if not  the shell try to interpolate non existent  nd variable

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For deleting the last N lines of a file  you can use the same concept of    sed  2 4d  file   You can use a combo with tail command to reverse the file  if N is 5    tail -r file   sed  1 5d  file   tail -r  gt  file   And this way runs also where head -n -5 file command doesn t run  like on a mac

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I came up with this  where n is the number of lines you want to delete   count  wc -l file  lines  expr   count  - n  head -n   lines  file  gt  temp txt mv temp txt file rm -f temp txt   It s a little roundabout  but I think it s easy to follow    Count up the number of lines in the main file Subtract the number of lines you want to remove from the count Print out the number of lines you want to keep and store in a temp file Replace the main file with the temp file Remove the temp file

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This will remove the last 3 lines from file   for i in   seq 1 3   do sed -i   d  file  done

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In docker  this worked for me  head --lines -N file path  gt  gt  file path

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If hardcoding n is an option  you can use sequential calls to sed  For instance  to delete the last three lines  delete the last one line thrice   sed   d  file   sed   d    sed   d

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Most of the above answers seem to require GNU commands extensions         head -n -2 myfile txt     -2  Badly formed number   For a slightly more portible solution        perl -ne  push  fifo     print shift  fifo  if  fifo  gt  10     OR       perl -ne  push  buf     END print  buf 0       buf-10      OR       awk   buf NR-1   0  END  for   i 0  i  lt   NR-10   i     print buf i         Where  10  is  n

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You can get the total count of lines with wc -l  lt file gt  and use  head -n  lt total lines - lines to remove gt   lt file gt

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I don t know about sed  but it can be done with head   head -n -2 myfile txt

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Just for completeness I would like to add my solution  I ended up doing this with the standard ed   ed -s sometextfile  lt  lt  lt    -2  d nwq    This deletes the last 2 lines using in-place editing  although it does use a temporary file in  tmp

User · Answer

To delete last 4 lines     nl -b a file   sort -k1 1nr   sed  1  4 d    sort -k1 1n   sed  s     0-9   t

[linux] How to use sed to remove the last n lines of a file

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