Improve Powershell Performance to Generate a Random File

Question

I\'d like to user Powershell to create a random text file for use in basic system testing (upload, download, checksum, etc). I\'ve used the following articles and co

Answer 1

If you are ok with punctuation you can use this:

Add-Type -AssemblyName System.Web
#get a random filename in the present working directory
$fn = [System.IO.Path]::Combine($pwd, [GUID]::NewGuid().ToString("N") + '.txt')
#set number of iterations
$count = 1mb/128
do{
  #Write the 1267 chars plus eol
  [System.Web.Security.Membership]::GeneratePassword(126,0) | Out-File $fn -Append ascii
  #decrement the counter
  $count--
}while($count -gt 0)

Which gets you to around 7 seconds. Sample Output:

0b5rc@EXV|e{kftc+1+Xn$-c%-*9q_9L}p=I=k@zrDg@HaJDcl}B(38i&m{lV@vlq%5h/a?m2X!yo]qs0=pEw:Tn4wb5F$k$O85$8F.QLvUzA{@X2-w%5(3k;BE2Qi

Using a stream writer instead of Out-File -Append avoids the open/close cycles and drops the same to 62 milliseconds.

Add-Type -AssemblyName System.Web
#get a random filename in the present working directory
$fn = [System.IO.Path]::Combine($pwd, [GUID]::NewGuid().ToString("N") + '.txt')
#set number of iterations
$count = 1mb/128
#create a filestream
$fs = New-Object System.IO.FileStream($fn,[System.IO.FileMode]::CreateNew)
#create a streamwriter
$sw = New-Object System.IO.StreamWriter($fs,[System.Text.Encoding]::ASCII,128)
do{
     #Write the 1267 chars plus eol
     $sw.WriteLine([System.Web.Security.Membership]::GeneratePassword(126,0))
     #decrement the counter
     $count--
}while($count -gt 0)
#close the streamwriter
$sw.Close()
#close the filestream
$fs.Close()

You could also use a stringbuilder, and GUIDs to generate pseudorandom numbers and lowercase.

#get a random filename in the present working directory
$fn = [System.IO.Path]::Combine($pwd, [GUID]::NewGuid().ToString("N") + '.txt')
#set number of iterations
$count = 1mb/128
#create a filestream
$fs = New-Object System.IO.FileStream($fn,[System.IO.FileMode]::CreateNew)
#create a streamwriter
$sw = New-Object System.IO.StreamWriter($fs,[System.Text.Encoding]::ASCII,128)
do{
    $sb = New-Object System.Text.StringBuilder 126,126
    0..3 | %{$sb.Append([GUID]::NewGuid().ToString("N"))} 2> $null
    $sw.WriteLine($sb.ToString())
    #decrement the counter
    $count--
}while($count -gt 0)
#close the streamwriter
$sw.Close()
#close the filestream
$fs.Close()

This takes about 4 seconds and generates the following sample:

1fef6ccabc624e4dbe13a0415764fd2c58aa873377c7465eaecabdf6ba6fdf71c55496600a374c4c8cff75be46b1fe474230231ffccc4e3aa2753391afb32c

If you are hell bent to use the same chars as in your sample you can do so with the following:

#get a random filename in the present working directory
$fn = [System.IO.Path]::Combine($pwd, [GUID]::NewGuid().ToString("N") + '.txt')
#array of valid chars
$chars = [char[]] ([char]'0'..[char]'9' + [char]'A'..[char]'Z' + [char]'a'..[char]'z')
#create a random object
$rand = New-Object System.Random
#set number of iterations
$count = 1mb/128
#get length of valid character array
$charslength = $chars.length
#create a filestream
$fs = New-Object System.IO.FileStream($fn,[System.IO.FileMode]::CreateNew)
#create a streamwriter
$sw = New-Object System.IO.StreamWriter($fs,[System.Text.Encoding]::ASCII,128)
do{
    #get 126 random chars This is the major slowdown
    $randchars = 1..126 | %{$chars[$rand.Next(0,$charslength)]}
    #Write the 1267 chars plus eol
    $sw.WriteLine([System.Text.Encoding]::ASCII.GetString($randchars))
    #decrement the counter
    $count--
}while($count -gt 0)
#close the streamwriter
$sw.Close()
#close the filestream
$fs.Close()

This takes ~27 seconds and generates the following sample:

Fev31lweOXaYKELzWOo1YJn8LpZoxonWjxQYhgZbR62EmgjHit5J1LrvqniBB7hZj4pNonIpoCZSHYLf5H63iUUN6UhtyOQKPSViqMTvbGUomPeIR36t1drEZSHJ6O

Indexing the char array and the out-file -Append opening and closing the file each time is a major slowdown.