Are there any easy ways to implement this function?

Yes of course. Write a subroutine which takes the following parameters: the variable that contains one line of data, the separator and a list of numbers (zero based!) of the columns to return. The subroutine returns a list containing the selected fields which you can save in an array. The subroutine returns a string of the fields extracted, joined by the same separator.

All you have to do now is write the body of this subroutine.

See how easy it is:

use Modern::Perl;

sub extract {
    my ($data, $separator, @fields) = @_;
    return join $separator, (split(/$separator/, $data))[@fields];
}

my $input = 'First#second#third#and this is field no. 4#FIVE5five5#all
+ sixes 666#Seventh and last';
my $extraction = extract($input, '#', 1, 3, 4, 6);
say $extraction;
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The subroutine does not do any error checking of the input parameters and will not deal correctly with escaped separators or quoted fields.

Update: I added a code example.

Update 2: amended the code example to return a string rather than a list