undef $/; # slurp mode
$^I = ""; # enable in-place editing

This sounds like a nice job for Tie::File. 

#!/usr/bin/perl -w
use Tie::File;
use strict;

my $max = 512;
my $file = 'syslog';

tie my @lines, 'Tie::File', $file;

my $size = 0;
for my $line (reverse -@lines .. -1) {
    if (($size += length $lines[$line]) > $max) {
        splice @lines, 0, (@lines + $line + 1);
        last;
    }
}

untie @lines;

[download]
(Didn't use negative splice length, because Tie::Splice seems to be unable to handle it.) 

U28geW91IGNhbiBhbGwgcm90MTMgY
W5kIHBhY2soKS4gQnV0IGRvIHlvdS
ByZWNvZ25pc2UgQmFzZTY0IHdoZW4
geW91IHNlZSBpdD8gIC0tIEp1ZXJk

In reply to Re: •Re: Limiting log file size by Juerd
in thread Limiting log file size by kardster

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • 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! —
  • 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:
    & &amp;
    < &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.