I wrote this script to update all the AssemblyInfo.cs files in a Visual Studio solution, to have the same version number. This is the kind of thing I would have used Perl to do, in the past. But Powershell's got this covered nicely.

[ 23 April 2008 - 1150am PST - I updated the script to deal with the AssemblyInfo.vb files in a VB project, and also to deal with version numbers that have less than 4 digits. Thanks for the suggestion, Jason! ]

Maybe someone can learn from this. 

# SetVersion.ps1
#
# Set the version in all the AssemblyInfo.cs or AssemblyInfo.vb files in any subdirectory.
#
# usage:  
#  from cmd.exe: 
#     powershell.exe SetVersion.ps1  2.8.3.0
# 
#  from powershell.exe prompt: 
#     .\SetVersion.ps1  2.8.3.0
#
# last saved Time-stamp: <Wednesday, April 23, 2008  11:46:40  (by dinoch)>
#


function Usage
{
  echo "Usage: ";
  echo "  from cmd.exe: ";
  echo "     powershell.exe SetVersion.ps1  2.8.3.0";
  echo " ";
  echo "  from powershell.exe prompt: ";
  echo "     .\SetVersion.ps1  2.8.3.0";
  echo " ";
}


function Update-SourceVersion
{
  Param ([string]$Version)
  $NewVersion = 'AssemblyVersion("' + $Version + '")';
  $NewFileVersion = 'AssemblyFileVersion("' + $Version + '")';

  foreach ($o in $input) 
  {
    Write-output $o.FullName
    $TmpFile = $o.FullName + ".tmp"

     get-content $o.FullName | 
        %{$_ -replace 'AssemblyVersion\("[0-9]+(\.([0-9]+|\*)){1,3}"\)', $NewVersion } |
        %{$_ -replace 'AssemblyFileVersion\("[0-9]+(\.([0-9]+|\*)){1,3}"\)', $NewFileVersion }  > $TmpFile

     move-item $TmpFile $o.FullName -force
  }
}


function Update-AllAssemblyInfoFiles ( $version )
{
  foreach ($file in "AssemblyInfo.cs", "AssemblyInfo.vb" ) 
  {
    get-childitem -recurse |? {$_.Name -eq $file} | Update-SourceVersion $version ;
  }
}


# validate arguments 
$r= [System.Text.RegularExpressions.Regex]::Match($args[0], "^[0-9]+(\.[0-9]+){1,3}$");

if ($r.Success)
{
  Update-AllAssemblyInfoFiles $args[0];
}
else
{
  echo " ";
  echo "Bad Input!"
  echo " ";
  Usage ;
}