Chances are good that by virtue of how the numeric data is getting into your script, Perl is seeing '1e-13' as a string, not a number. You can see this happening here:

perl -e "print q/2e+11/, $/; print 2e+11, $/;"
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You can coerce it back to a number by treating it like one. One way is by adding zero to it:

perl -e "print q/2e+11/ + 0, $/;"
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And here is that theory applied to an example that may more closely resemble your problem code.

my @numbers;
while( my $num = <DATA> ) {
    chomp $num;
    push @numbers, $num + 0;
}
print "$_\n" for sort { $a <=> $b } @numbers;
__DATA__
1e-13
2e-18
1e-11
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I hope this is on the right track. ;)

That's a good theory, but the spaceship operator $a <=> $b coerces its argument into integers numbers, so this shouldn't matter. Indeed, run your code without the + 0 or simply

perl -le'$,="\n"; print sort {$a<=>$b} qw(1e-13 2e-18 1e-11)'
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and you will see that the output is the same.

This is somewhat tangetial, but in a numerical context perl will coerce any string that begins with something recognizable as a number into a number. That's why "0 but true" is a perfectly good¹ "true zero." See Is '2x' + '3y' == 5 documented? and the man page for the C atof function.

¹Well, not quite. As it turns out '0 but true' has a "special dispensation" that disables the warnings that perl would have otherwise have generated. E.g.:

% perl -wle 'print "OK" if "0 but true" < 1'
OK
% perl -wle 'print "OK" if "0 but righteous" < 1'
Argument "0 but righteous" isn't numeric in numeric lt (<) at -e line 
+1.
OK
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the lowliest monk

sort {$a<=>$b}
           ^--- $ here
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sorry for the late reply guys. You know what, it does work if i just manually feed it into the array. WIll have to see why its not sorting when i pick it up from the data file. I'll post some sample data and the code tonite, if it still doesn't work.

sorted out the problem...it was a problem in the file. thanks a lot guys.

#!perl -l

$, = ' ';

my @n = qw/ 1e-13 2e-14 3e-15 4e-16 /;
print sort @n;
print sort { $a <=> $b } @n;

@n = (1e-13, 2e-14, 3e-15, 4e-16);
print sort @n;
print sort { $a <=> $b } @n;

__END__

1e-13 2e-14 3e-15 4e-16
4e-16 3e-15 2e-14 1e-13
1e-13 2e-14 3e-15 4e-16
4e-16 3e-15 2e-14 1e-13
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