use IO::File;

my $fh = new IO::File "input_file", "r";

my @lines = <$fh>;

my $pattern = "r145";

my ($para,@output);

foreach my $line(@lines) {
    if($line =~ /^(\S+)/  ) {
        if($line =~ /^$pattern/) {
            $para = undef;
        } else {
            $para = $1;
            push @output,$line;
        }
    } elsif(defined($para) ) {
        push @output,$line;
    }
}

print @output;