The first thing you should ask yourself is whether the line to be split has its fields always on the same position ("fixed length fields") or whether the fields are somehow delimited by some or other "marker" (such as -perhaps- the space, underscore character or the minus-sign).

If it is fixed length, unpack is where you have to look first. If the record has delimited fields (of possibly varying lengths), split or a regular expression is more likely to help you.

A tentative solution for delimited fields is:

use strict;

my $line
    = 'Experiment: rs5443-61902_923_922_921_291008 Active filters: FAM
+ (483-533), VIC /HEX / Yellow555 (523-568)';

my ( undef, $first, $second, undef, undef, undef, $third, undef )
    = split /[- _]/, $line;

print "First: $first\nSecond: $second\nThird: $third\n";
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Which gives:

First: rs5443
Second: 61902
Third: 291008
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