use strict;
use warnings;

my @string = ('String A', 'String B', 'String C', 'String D', 'String E');
my @logfile = ('A.log', 'B.log', 'C.log', 'D.log', 'E.log');
my @logfh;

open (IN, '<', 'input.txt') or die "Couldn't open input file!\n";

for my $i (0..$#logfile) {
    open ($logfh[$i], '>', $logfile[$i]) or die "Couldn't create logfile!\n";
}

local $/ = '';
while (my $paragraph = <IN>) {
    for my $i (0..$#string) {
        if ( index($paragraph, $string[$i]) >= 0) {
            print {$logfh[$i]} $paragraph;
        }
    }
}
close IN;

foreach my $fh (@logfh) {
    close $fh;
}