#!/usr/bin/perl
use strict;
use warnings;

my @buffer;   # a queue data structure

while ( <DATA> ) {
    if ( /I sent/ ) {
        print @buffer;          # 3 lines before
        print;                  # the matching line
        print scalar(<DATA>);   # 1 line following
        last;                   # all done
}
push @buffer, $_;
shift @buffer if @buffer > 3;
}


__DATA__
this is
the output
from
the command
I sent
to the
command interperter
[download]