My first reaction was to split and grep, but since the numbers are so tightly defined, I think a regex should do,

my @keepers;
open my $fh, '<', '/path/to/file.dat' or die $!;
while (<$fh>) {
    while ( /(\d+\.\d+)/g ) {
        push @keepers, $_ and last
            if $1 >= 296.1 && $1 <= 314.0;
    }
}
close $fh or die $!;
[download]

The while (/(foo)/g) construction loops over all the matches, putting the matching text in $1.

Update: Missed the exclusion for 305.1, grep it is:

my @keepers;
open my $fh, '<', '/path/to/file.dat' or die $!;
while (<$fh>) {
    my @data = grep {
        /^\d+\.\d+$/ &&  $_ >= 296.1 && $_ <= 314.0
    } split ',';
    if (@data) {
        push @keepers, $_ 
            unless @data == 1 and $data[0] eq '305.1';
    }
}
close $fh or die $!;
[download]

Update2: CountZero++ is correct, code amended.

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.