create-large-file.p6

#!/usr/bin/env perl6

# note: a run on juvat2 (2016-01-31) with 10 Gb was ~36 minutes

# 100 char string (counting the ending newline)
my $str = "012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678\n";
my $gb  = 1_000_000_000;

my $prog = $*PROGRAM.basename;
if !@*ARGS.elems {
  say "Usage: $prog <file size in Gb (an integer > -1)>\n";
  exit;
}

# desired size in gigabytes
my $ngb = shift @*ARGS;
$ngb .= Int;
#say $ngb.WHAT;

die "FATAL: '$ngb' is not an integer.\n"
  if $ngb.WHAT !~~ Int;

my $ofil = 'large-' ~ $ngb ~ '-gb-file.txt';

# how many (lines) iterations needed?
my $slen   = $str.chars;
my $nlines = $ngb * $gb / $slen;

# if we create a small file for testing
my $snlines = 100_000;
my $ssize  = $snlines * $slen / 1_000_000; # Mb

my $ostr = $ngb == 0 ?? "0 ($ssize Mb)" !! $ngb;
$nlines = $snlines if $ngb == 0;

say "Requested file size (Gb): $ostr";
say "String size:  $slen";
say "Number lines: $nlines";

my $fp = open($ofil, :w);

for 1 .. $nlines {
  $fp.print($str);
}

say "see output file '$ofil'";