#! perl
use strict;
use warnings;

my $target = $ARGV[0] - 1;
my $text   = <<'LIST';
#EXTM3U
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=80000
80.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=400000
400.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=700000
700.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1500000
1500.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=2500000
2500.m3u8
LIST

my $entry = qr{ \#EXT-X-STREAM-INF:PROGRAM-ID= \d+ 
                ,BANDWIDTH= \d+ \s+ \d+\.m3u8 \s+ }xms;

if ($text =~ m{
                ( \A  \#EXTM3U \s+     )    #1
                ( (?: $entry){$target} )    #2
                ( (?: $entry)          )    #3
                ( (?: $entry)*         )    #4
              }xms)
{
    print "$1$3$2$4";
}
else
{
    print "No match found\n";
}

##</code><code>##

12:57 >perl 710_SoPW.pl 3
#EXTM3U
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=700000
700.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=80000
80.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=400000
400.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1500000
1500.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=2500000
2500.m3u8

12:57 >