use strict;
use warnings;
use Data::Dump qw( pp );

my $ref = [ {} ];
my $prev_prefix = '';

while (<DATA>) {
  my ( $prefix, $text ) = split /> ?/;
  if ( $prefix gt $prev_prefix ) {
    $ref->[-1]{$prefix} = $text;
  }
  elsif ( $prefix eq $prev_prefix ) {
    $ref->[-1]{$prefix} .= $text;
  }
  else {
    push @$ref, { $prefix => $text };
  }
  $prev_prefix = $prefix;
}

pp $ref;

__DATA__
a> some random text
b> 
b> a few random
b> lines
b> 
b> of more 
b> random
b> 
b> text
c> some more 
c> 
c> random
c> text
c> 
a> some random text
b> 
b> a few random
b> lines
b> 
b> of more 
b> random
b> 
b> text
c> some more 
c> 
c> random
c> text
c>