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

my @values; 

while (<DATA>) {
    my ($line) = $_;
    chomp($line);
    if ( $line =~ m/^address/ ) {
        push @values, split( ' st ', $line );
    }
    else {
        print $line, $/;
    }
}

print $_, ' st', $/ foreach @values;

__DATA__
This is the list of address
here are the addreses
address 6433 main st address 6434 main st address 6435 main st