-A NUM, --after-context=NUM
              Print NUM lines  of  trailing  context  after  matching  lines.
              Places  a  line  containing  --  between  contiguous  groups of
              matches.

       -B NUM, --before-context=NUM
              Print  NUM  lines  of  leading  context  before matching lines.
              Places a  line  containing  --  between  contiguous  groups  of
              matches.

sub lines_grep{
my($pattern,$line,$flag,$n,@tmp)=(@_);
while(<DATA>){
	if($_=~/$pattern/){
		print @tmp;	
		$flag=1;
	}
	else{
		if($#tmp < $line-1){
			push @tmp, $_;
		}
		else{
			shift @tmp;
			push @tmp, $_;
		}
	}
	if ($flag==1){
		print $_ ;
		$n++;
	}
	if($n>$line){
		last;
	}
}
}
#lines_grep(pattern,3);
lines_grep(4,2);
__DATA__
1
2
3
4
pattern
6
7
8
9