The combination of join and grep sounds like it will do what you want. (map and sort and some of their friends from List::Util and List::MoreUtils are also often useful, but don't sound needed in your case.)

The following example uses join and grep to filter the numbers from 1 to 20 for primes, then join the primes together into a string separated by semicolons.

sub is_prime
{
   my $num = shift;
   return if $num == 1;  # 1 is not prime
   
   die "usage: is_prime(NATURAL NUMBER)"
      unless $num =~ /^[1-9][0-9]*$/;
   
   for my $div (2 .. sqrt $num)
   {
      return if $num % $div == 0;
   }
   return 1;
}

my @numbers = 1 .. 20;

print join ";", grep { is_prime($_) } @numbers;

[download]
perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re^2: Analyse an array and join only some elements of it by tobyink
in thread Analyse an array and join only some elements of it by Istirion

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