3 MB is not huge. In the context of terrabyte drives and multiple GB of physical memory it is in fact trivial! Assembling your output image in memory by simply concatenating copies of the input file on to the end of a string, then printing the resulting string to your output file is likely to be fast and easy to code. length then can be used to calculate how many copies you need and how big your output image is currently.

However, depending on the contents of the file and how it will be processed, assembling a test file in this fashon seems highly dubious to me! You would probably be better to figure out a way of generating realistic data that will provide a though test set for your benchmarking tests. If the code being tested behaves differently for the first instance of a record than for subsequent occurrences, or if different record data is more expensive (in terms of processor time) than other data then your multiple copy data file may introduce nasty biases in the benchmark results.

Kinda unwieldy, but on win you could use (wrapped):

perl -e"$f=-s($ARGV[0]); $n=1+int($ARGV[1]*1024**3)/$f;
system 'copy ' . join'+', $ARGV[0] x $n . ' huge.txt'" sample.txt 1
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There's probably a similar formulation for *nix.

Did you even actually try to change your pseudocode into a perl script? It looks as though you've been given a task to do at work and just pasted your requirements here.

The size requirement of 3MB + is not all that large, so default output buffering should be good enough.

-- Roman

Is it imperative that you use flatfiles? Or could something like SQLite be used instead?

#!/usr/bin/perl


use strict;
use warnings;
use Carp;


sub loaddict {    
    my $dict = shift;
    
    open my $fh, $dict or croak "can't open $dict: $!";
    my @words = <$fh>;
    chomp @words;
        
    return \@words;
}

#######################
# main

my $testdir = $ARGV[0] 
    or die "usage : $0 <test folder> <number of files>";
    
my $filecount = $ARGV[1] 
    or die "usage : $0 <test folder> <number of files>";

my $seed = 0;
$seed = $ARGV[2] if defined  $ARGV[2];

# force number
$filecount += 0;

if ( not -d "$testdir" ) {
    mkdir "$testdir" or die "can't mkdir $testdir";
}

my $wordlist = loaddict("/usr/share/dict/words");
srand(42 + $seed );

for ( 1 .. $filecount ) {
    open my $file, '>', "$testdir/$_" or croak "can't open file : $!";
    
    my $filesize = int( rand(10000) ) + 5000 ;
    for ( 1 .. $filesize ) {
        my $dice = int( rand($#{$wordlist}) ) ;
        print $file $wordlist->[$dice] . " ";
        if ( $_ % 12 == 0 ) {
            print $file "\n";
        }
    }
}
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