Remove the last line from a file in Bash

Question

I have a file  foo txt  containing the following lines   a b c   I want a simple command that results in the contents of foo txt being   a b

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Ruby 1 9    ruby -ne  BEGIN prv     print prv   prv      file

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OK processing a good amount of data and the output was OK  but had one junk line  If I piped the output of the script to    sed -i    d    I would get the following error and finally no output at all sed  no input files But    head -n -1   worked

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Mac Users   if you only want the last line deleted output without changing the file itself do  sed -e    d  foo txt  if you want to delete the last line of the input file itself do  sed -i    -e    d  foo txt

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To remove the last line from a file without reading the whole file or rewriting anything  you can use  tail -n 1   file    wc -c   xargs -I    truncate   file  -s -     To remove the last line and also print it on stdout   pop  it   you can combine that command with tee   tail -n 1   file    tee  gt  wc -c   xargs -I    truncate   file  -s -      These commands can efficiently process a very large file   This is similar to  and inspired by  Yossi s answer  but it avoids using a few extra functions     If you re going to use these repeatedly and want error handling and some other features  you can use the poptail command here  https   github com donm evenmoreutils

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You can try this method also   example of removing last n number of lines   a 0   while    a -lt 4   do sed -i    d  output txt  a expr  a   1 done  Removing last 4 lines from file output txt

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Linux    is the last line  d for delete   sed   d    path to your file name   MacOS  Equivalent of the sed -i  sed -i    -e    d    path to your file name

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awk  NR gt 1 print buf  buf    0     Essentially  this code says the following   For each line after the first  print the buffered line  for each line  reset the buffer  The buffer is lagged by one line  hence you end up printing lines 1 to n-1

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Here s how you can do it manually  I personally use this method a lot when I need to quickly remove the last line in a file    vim    FILE    That   sign there means that when the file is opened in the vim text editor  the cursor will be positioned on the last line of the file   Now just press d twice on your keyboard  This will do exactly what you want   remove the last line  After that  press   followed by x and then press Enter  This will save the changes and bring you back to the shell  Now  the last line has been successfully removed

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Here is a solution using sponge  from the moreutils package   head -n -1 foo txt   sponge foo txt  Summary of solutions   If you want a fast solution for large files  use the efficient tail or dd approach   If you want something easy to extend tweak and portable  use the redirect and move approach   If you want something easy to extend tweak  the file is not too large  portability  i e   depending on moreutils package  is not an issue  and you are a fan of square pants  consider the sponge approach    A nice benefit of the sponge approach  compared to  quot redirect and move quot  approaches  is that sponge preserves file permissions  Sponge uses considerably more RAM compared to the  quot redirect and move quot  approach  This gains a bit of speed  only about 20    but if you re interested in speed the  quot efficient tail quot  and dd approaches are the way to go

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For Mac Users    On Mac  head -n -1 wont work  And  I was trying to find a simple solution   without worrying about processing time   to solve this problem only using  head  and or  tail  commands   I tried the following sequence of commands and was happy that I could solve it just using  tail  command   with the options available on Mac    So  if you are on Mac  and want to use only  tail  to solve this problem  you can use this command       cat file txt   tail -r   tail -n  2   tail -r   Explanation    1  tail -r   simply reverses the order of lines in its input  2  tail -n  2   this prints all the lines starting from the second line in its input

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awk  NR     wc -l  lt  text file   text file   gt  text file   This snippet does the trick

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echo -e   d nw nq   ed foo txt

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This is by far the fastest and simplest solution  especially on big files    head -n -1 foo txt  gt  temp txt   mv temp txt foo txt   if You want to delete the top line use this   tail -n  2 foo txt   which means output lines starting at line 2   Do not use sed for deleting lines from the top or bottom of a file -- it s very very slow if the file is large

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Using GNU sed   sed -i    d  foo txt   The -i option does not exist in GNU sed versions older than 3 95  so you have to use it as a filter with a temporary file   cp foo txt foo txt tmp sed    d  foo txt tmp  gt  foo txt rm -f foo txt tmp   Of course  in that case you could also use head -n -1 instead of sed   MacOS   On Mac OS X  as of 10 7 4   the equivalent of the sed -i command above is  sed -i    -e    d  foo txt

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I had trouble with all the answers here because I was working with a HUGE file   300Gb  and none of the solutions scaled  Here s my solution   dd if  dev null of  lt filename gt  bs 1 seek   echo   stat --format  s  lt filename gt    -    tail -n1  lt filename gt    wc -c    bc     In words  Find out the length of the file you want to end up with  length of file minus length of length of its last line  using bc  and  set that position to be the end of the file  by dding one byte of   dev null onto it     This is fast because tail starts reading from the end  and dd will overwrite the file in place rather than copy  and parse  every line of the file  which is what the other solutions do   NOTE  This removes the line from the file in place  Make a backup or test on a dummy file before trying it out on your own file

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Both of these solutions are here in other forms  I found these a little more practical  clear  and useful   Using dd   BADLINESCOUNT 1 ORIGINALFILE  tmp whatever dd if   ORIGINALFILE  of   ORIGINALFILE  tmp status none bs 1 count   printf    stat --format  s   ORIGINALFILE   -   tail -n  BADLINESCOUNT    ORIGINALFILE    wc -c  n    bc    bin mv -f   ORIGINALFILE  tmp   ORIGINALFILE    Using truncate   BADLINESCOUNT 1 ORIGINALFILE  tmp whatever truncate -s   printf    stat --format  s   ORIGINALFILE   -   tail -n  BADLINESCOUNT    ORIGINALFILE    wc -c  n    bc     ORIGINALFILE

[bash] Remove the last line from a file in Bash

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