one-liner: print all lines except the last 3?

Question

I would like to simulate GNU\'s head -n -3, which prints all lines except the last 3, because head on FreeBSD doesn\'t have this feature. So I am t

Answer 1

This works with a pipe as well as an input file:

seq 1 10 | perl -e'@x=<>;print@x[0..$#x-3]'

Answer 2

seq 1 10 | perl -ne 'push @l, $_; print shift @l if @l > 3'

Answer 3

Here's a late answer, because I was running into something like this yesterday.

This solution is:

• pure bash
• one-liner
• reads the input stream only once
• reads the input stream line-by-line, not all at once

Tested on Ubuntu, Redhat and OSX.

$ seq 1 10 | { n=3; i=1; while IFS= read -r ln; do [ $i -gt $n ] && cat <<< "${buf[$((i%n))]}"; buf[$((i%n))]="$ln"; ((i++)); done; }
1
2
3
4
5
6
7
$ 

It works by reading lines into a circular buffer implemented as an n-element array.

n is the number of lines to cut off the end of the file.

For every line i we read, we can echo the line i-n from the circular buffer, then store the line i in the circular buffer. Nothing is echoed until the first n lines are read. (i mod n) is the index into the array which implements the circular buffer.

Because the requirement is for a one-liner, I tried to make it fairly brief, unfortunately at the expense of readability.

Answer 4

seq 1 10 | perl -e '@x=("")x3;while(<>){print shift @x;push @x,$_}'

or

perl -e '@x=("")x3;while(<>){print shift @x;push @x,$_}' file

or

command | perl -pe 'BEGIN{@x=("")x3}push @x,$_;$_=shift @x'
perl -pe 'BEGIN{@x=("")x3}push @x,$_;$_=shift @x' file

Answer 5

Or do it with bash alone if you have version 4.0 or newer:

seq 1 10 | (readarray -t LINES; printf '%s\n' "${LINES[@]:(-3)}")

Update: This one would remove the last three lines instead of showing only them.

seq 1 10 | (readarray -t L; C=${#L[@]}; printf '%s\n' "${L[@]:0:(C > 3 ? C - 3 : 0)}")

For convenience it could be placed on a function:

function exclude_last_three {
    local L C
    readarray -t L; C=${#L[@]}
    printf '%s\n' "${L[@]:0:(C > 3 ? C - 3 : 0)}"
}

seq 1 10  | exclude_last_three
seq 11 20 | exclude_last_three

Answer 6

This awk one-liner seems to do the job:

awk '{a[NR%4]=$0}NR>3{print a[(NR-3)%4]}' file