I must admit, the lazy side of me did not want to do the mental hacking that your module change suggested when the required solution seemed so simple in the first place. I can imagine that you have some rather large datasets that, for performance reasons, you would rather access via iteration (Tie) than by sucking everything into memory. That gives a little better justification for fooling around with Tie.

Where a module encapsulates several steps, and your inexperienced user knows exactly what to expect from said module, by all means use it. The trick comes when you change the rules (i.e. change the module) that the inexperienced user knows. By adapting the module for the special formats of the bioinformatics world, aren't you requiring an extra level of understanding? Whereas by being self-sufficient and learning the basics of Perl, "the 'official' language of bioinformatics", isn't the inexperienced user better positioned to handle whatever data processing need arises? Or have the minimal foundation necessary to glue in an appropriate Bio module from CPAN?

For getting a random line, while it may be wasteful of computer resources, it's certainly straightforward to simply do:

#open INFILE, '<', 'outfile.txt' or die "Could not open 'outfile.txt':
+  $!\n";
#my @seq_info = <INFILE>;
#close INFILE;

my @seq_info = <DATA>;
print $seq_info[int rand ($#seq_info)];


__DATA__
seq_1    1    33    gene
seq_1    1    20    exon
seq_1    21    27    exon
seq_1    28    33    exon
seq_2    1    80    gene
seq_2    1    80    exon
seq_3    1    55    gene
seq_3    1    30    exon
seq_3    31    50    exon
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