In that case, to a first approximation you could do something like the following:

#! /usr/bin/perl -w

use strict;

while( <DATA> ) {
    chomp;

    my $nr = squeeze($_);
    print "[$nr] $_\n";
}

sub squeeze {
  my $n = sprintf( '%0.8f', $_[0] );
  $n =~ s/^0//;
  substr( $n, 0, 8 );
}

__DATA__
12345678901234567890
1234567890
1234567.0
1234567.9
123456.789012345
12345
123.4567
123.4
.1
.1234567890
0.00000999999
[download]

Then again, the few test cases here reveal a certain number of bugs. I contend that the results to squeeze() contain a bug, in that 1234567.0 and 1234567.9 return the same results, but in truth the latter should return 1234568. I don't know whether you will hit these borderline cases or not.

Maybe there's yet another module that deals with your problem.

<update>In response to gjb's remark about whether this code is a good idea or not, I was trying to point out the folly of storing numbers in fixed-width fields. The idea being that when you see what this outputs, maybe you better start thinking about overflow conditions. As I don't know the domain. I can't really deal with in a satisfactory matter (at least to my standards). I prefer to let the code stand as it is.</update>

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