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foreach my $elA (@arA) {
    foreach my $elB (@arB) {
...
        }
    }
}

foreach my $elA (@arA) {
    map { ($elA eq $_) and push @{$all{$elA}}, "$_ - from Array B" } @
+arB;
    map { ($elA eq $_) and push @{$all{$elA}}, "$_ - from Array C" } @
+arC;
}

#!/usr/bin/perl -w

...

print Dumper %all;
# Then do some other things with %all...