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How do I delete the last n lines of an ascii file using shell commands?

chaos
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user137256
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3 Answers3

13

With head (removes the last 2 lines):

head -n -2 file

With sed/tac (removes the last 2 lines):

tac file | sed "1,2d" | tac

tac reverses the file, sed deletes (d) the lines 1 to 2 (2 can be any number).

chaos
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    Why is it when I try redirecting the output back into the file (OP asked to delete the lines of the file, after all), I just get a blanked file: `$ head -n -2 test-file > test-file` When I pick another file name, the `head` output redirects as I would expect? What's the best way to do the redirect into the same file? – user1717828 Oct 06 '15 at 13:37
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    @user1717828 The problem is that `bash` processes the redirections first, then executes the command. When `>file` is processed bash creates (if not existing) an empty file, else it is truncated. `head` then prints nothing because the file it reads is empty. You have to go via a temporary file. `head -n -2 file >tmp && mv tmp file`. BTW: all tools which allow "inplace editing" (like `sed -i`, `gawk -i inplace`, `perl -i`) do exactly the same. – chaos Oct 06 '15 at 13:53
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    `head -n -2` is great but is not supported by all versions of head, in particular the bsd version that ships with mac os :-( – phs Aug 04 '16 at 09:29
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Have a look at the manpage for head - you can specify a number of lines, and it will give you that many lines out of a file.

head -10 filename

Gives first 10 lines of a file. If you don't know how long your file is, you can use wc -l to count the number of lines. And then use head to print the appropriate number.

Sobrique
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-2
tac file| sed -i 'nd' | tac

tac reverses the file, sed deletes (d) the lines n numbers of lines

Anthon
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harekrushna
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