This part of your code:

while (<FH>) {
   chomp $_;
   $a[$i]=$_;
   $i++;
}
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Can be rendered in a variety of briefer ways, briefest of which is probably:

@a = <FH>;  # diamond operator in "list" (or array) context
            # will read all input records into array elements
chomp @a;   # chomp can work on a list
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If there are other things you want to do while assigning input records to an array, you can keep the while loop, but without using the array index variable ($i):

while (<FH>) {
   chomp;        # $_ is the default arg to chomp;
     # ... do other things to $_ if necessary ...

   push @a, $_;  # add a new element at end of @a
}
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In terms of printing the array elements as a "joined set", you should just play with different things to see how they work -- try a few command lines like this:

 perl -e '@a=qw/one two three four/; print @a,$/'

 perl -e '@a=qw/one two three four/; print "@a$/"'

 perl -e '@a=qw/one two three four/; print join(" ", map { "foo=$_" } 
+@a), $/'
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R some more FMs and have fun with it.