$ perl -Mstrict -Mwarnings -E '
open my $inFH, q{<}, \ <<EOD or die $!;
line 1
line 2
line 3
line 4
line 5
line 6
line 7
line 8
line 9
EOD

my $lineBeforeMatch = 5;
my @prevLines;

my $lookFor = qr{line 7};

while ( <$inFH> )
{
    push @prevLines, $_;
    shift @prevLines if $#prevLines > $lineBeforeMatch;
    print $prevLines[ 0 ] if m{$lookFor};
}'
line 2
$