Delete nth line (when counted from the bottom)

Using awk

Try:

$ awk '/Start to grab/,/^$/' prova.txt
Start to grab from here: 1
random1
random2
random3
random4

Start to grab from here: 2
random1546
random2561

Start to grab from here: 3
random45
random22131

/Start to grab/,/^$/ defines a range. It starts with any line that matches Start to grab and ends with the first empty line, ^$, that follows.

Using sed

With very similar logic:

$ sed -n '/Start to grab/,/^$/p' prova.txt
Start to grab from here: 1
random1
random2
random3
random4

Start to grab from here: 2
random1546
random2561

Start to grab from here: 3
random45
random22131

-n tells sed not to print anything unless we explicitly ask it to. /Start to grab/,/^$/p tells it to print any lines in the range defined by /Start to grab/,/^$/.

Keep state on whether to print the previous line, edit said to remove the comma when necessary. This method only keeps one or two lines of the file in memory.

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

my $printing = 1;
my $previous;

# reads from standard input (optionally with the conventional -) or from
# the named files
shift @ARGV if @ARGV == 1 and $ARGV[0] eq '-';
while ( my $line = readline ) {
    if ( $line =~ m/^\s+PRIMARY KEY/ ) {
        $previous =~ s/,[ \t]*$//;
        $printing = 0;
    } elsif ( $line =~ m/^\) ENGINE/ ) {
        $printing = 1;
    } elsif ( !$printing ) {
        undef $previous;
    }
    print $previous if defined $previous;
    $previous = $line if $printing;
}
# don't forget last line after fall off the end of input (eof)
print $previous if defined $previous;