I use the following short perl script to shuffle the lines in a file (to produce lists of random strings for testing): 
#!/usr/bin/perl -w  
use strict;

open(IN, "<".$ARGV[0]);
my @lines = <IN>;
close(IN);

shuffle(\@lines);
print $_ foreach (@lines);

sub shuffle {
    my $array = shift;
    my $i = $#{$array}+1;
    while ($i != -1) {
        $i--;
        my $j = int rand ($i+1);
        next if $i==$j;
        @$array[$i,$j]=@$array[$j,$i];
    }
}

[download]
When I run this on a 70mb file, ~11 million lines, this eats about 1.5 gigs of ram (all I have left) then hits "Out of Memory!" before it's finished reading the file.

I have swap disabled, I suppose that would allow me to run this. However, I'm curious -- why does it need so much memory to store 70mb of data? Is there anything I can do here? I tried presizing the array to 12 million, that did not make any difference (can I presize each element, eg, request a block of a given size?).

In reply to mem usage by halfcountplus

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.