Powershell script to find and replace file contents

Replace-FileString.ps1

# Replace-FileString.ps1
# Written by Bill Stewart (bstewart@iname.com)
# Modified by Matthew Steeples (matthew@mercuryit.co.uk) to enable using the 
# -Recurse flag on Get-ChildItem and piping in
#
# Replaces strings in files using a regular expression. Supports
# multi-line searching and replacing.

#requires -version 2

<#
.SYNOPSIS
Replaces strings in files using a regular expression.

.DESCRIPTION
Replaces strings in files using a regular expression. Supports
multi-line searching and replacing.

.PARAMETER Pattern
Specifies the regular expression pattern.

.PARAMETER Replacement
Specifies the regular expression replacement pattern.

.PARAMETER Path
Specifies the path to one or more files. Wildcards are permitted. Each
file is read entirely into memory to support multi-line searching and
replacing, so performance may be slow for large files.

.PARAMETER LiteralPath
Specifies the path to one or more files. The value of the this
parameter is used exactly as it is typed. No characters are interpreted
as wildcards. Each file is read entirely into memory to support
multi-line searching and replacing, so performance may be slow for
large files.

.PARAMETER CaseSensitive
Specifies case-sensitive matching. The default is to ignore case.

.PARAMETER Multiline
Changes the meaning of ^ and $ so they match at the beginning and end,
respectively, of any line, and not just the beginning and end of the
entire file. The default is that ^ and $, respectively, match the
beginning and end of the entire file.

.PARAMETER UnixText
Causes $ to match only linefeed (\n) characters. By default, $ matches
carriage return+linefeed (\r\n). (Windows-based text files usually use
\r\n as line terminators, while Unix-based text files usually use only
\n.)

.PARAMETER Overwrite
Overwrites a file by creating a temporary file containing all
replacements and then replacing the original file with the temporary
file. The default is to output but not overwrite.

.PARAMETER Force
Allows overwriting of read-only files. Note that this parameter cannot
override security restrictions.

.PARAMETER Encoding
Specifies the encoding for the file when -Overwrite is used. Possible
values are: ASCII, BigEndianUnicode, Unicode, UTF32, UTF7, or UTF8. The
default value is ASCII.

.INPUTS
System.IO.FileInfo.

.OUTPUTS
System.String without the -Overwrite parameter, or nothing with the
-Overwrite parameter.

.LINK
about_Regular_Expressions

.EXAMPLE
C:\>Replace-FileString.ps1 '(Ferb) and (Phineas)' '$2 and $1' Story.txt
This command replaces the string 'Ferb and Phineas' with the string
'Phineas and Ferb' in the file Story.txt and outputs the file. Note
that the pattern and replacement strings are enclosed in single quotes
to prevent variable expansion.

.EXAMPLE
C:\>Replace-FileString.ps1 'Perry' 'Agent P' Ferb.txt -Overwrite
This command replaces the string 'Perry' with the string 'Agent P' in
the file Ferb.txt and overwrites the file.
#>

[CmdletBinding(DefaultParameterSetName="Path",
               SupportsShouldProcess=$TRUE)]
param(
  [parameter(Mandatory=$TRUE,Position=0)]
    [String] $Pattern,
  [parameter(Mandatory=$TRUE,Position=1)]
    [String] [AllowEmptyString()] $Replacement,
  [parameter(Mandatory=$TRUE,ParameterSetName="Path",
    Position=2,ValueFromPipeline=$TRUE, ValueFromPipelineByPropertyName=$TRUE)]
    
    [String[]] $FullName,
  [parameter(Mandatory=$TRUE,ParameterSetName="LiteralPath",
    Position=2)]
    [String[]] $LiteralPath,
    [Switch] $CaseSensitive,
    [Switch] $Multiline,
    [Switch] $UnixText,
    [Switch] $Overwrite,
    [Switch] $Force,
    [String] $Encoding="ASCII"
)

begin {
  # Throw an error if $Encoding is not valid.
  $encodings = @("ASCII","BigEndianUnicode","Unicode","UTF32","UTF7",
                 "UTF8")
  if ($encodings -notcontains $Encoding) {
    throw "Encoding must be one of the following: $encodings"
  }

  # Extended test-path: Check the parameter set name to see if we
  # should use -literalpath or not.
  function test-pathEx($FullName) {
    switch ($PSCmdlet.ParameterSetName) {
      "Path" {
        test-path $FullName
      }
      "LiteralPath" {
        test-path -literalpath $FullName
      }
    }
  }

  # Extended get-childitem: Check the parameter set name to see if we
  # should use -literalpath or not.
  function get-childitemEx($FullName) {
    switch ($PSCmdlet.ParameterSetName) {
      "Path" {
        get-childitem $FullName -force
      }
      "LiteralPath" {
        get-childitem -literalpath $FullName -force
      }
    }
  }

  # Outputs the full name of a temporary file in the specified path.
  function get-tempname($FullName) {
    do {
      $tempname = join-path $FullName ([IO.Path]::GetRandomFilename())
    }
    while (test-path $tempname)
    $tempname
  }

  # Use '\r$' instead of '$' unless -UnixText specified because
  # '$' alone matches '\n', not '\r\n'. Ignore '\$' (literal '$').
  if (-not $UnixText) {
    $Pattern = $Pattern -replace '(?<!\\)\$', '\r$'
  }

  # Build an array of Regex options and create the Regex object.
  $opts = @()
  if (-not $CaseSensitive) { $opts += "IgnoreCase" }
  if ($MultiLine) { $opts += "Multiline" }
  if ($opts.Length -eq 0) { $opts += "None" }
  $regex = new-object Text.RegularExpressions.Regex $Pattern, $opts
}

process {
  # The list of items to iterate depends on the parameter set name.
  switch ($PSCmdlet.ParameterSetName) {
    "Path" { $list = $FullName }
    "LiteralPath" { $list = $LiteralPath }
  }

  # Iterate the items in the list of paths. If an item does not exist,
  # continue to the next item in the list.
  foreach ($item in $list) {
    if (-not (test-pathEx $item)) {
      write-error "Unable to find '$item'."
      continue
    }

    # Iterate each item in the path. If an item is not a file,
    # skip all remaining items.
    foreach ($file in get-childitemEx $item) {
      if ($file -isnot [IO.FileInfo]) {
        write-error "'$file' is not in the file system."
        break
      }

      # Get a temporary file name in the file's directory and create
      # it as a empty file. If set-content fails, continue to the next
      # file. Better to fail before than after reading the file for
      # performance reasons.
      if ($Overwrite) {
        $tempname = get-tempname $file.DirectoryName
        set-content $tempname $NULL -confirm:$FALSE
        if (-not $?) { continue }
        write-verbose "Created file '$tempname'."
      }

      # Read all the text from the file into a single string. We have
      # to do it this way to be able to search across line breaks.
      try {
        write-verbose "Reading '$file'."
        $text = [IO.File]::ReadAllText($file.FullName)
        write-verbose "Finished reading '$file'."
      }
      catch [Management.Automation.MethodInvocationException] {
        write-error $ERROR[0]
        continue
      }

      $replace = $regex.Replace($text, $Replacement)
      # If -Overwrite not specified, output the result of the Replace
      # method and continue to the next file.
      if (-not $Overwrite) {
        Out-Host $replace
        continue
      }

      # Do nothing further if we're in 'what if' mode.
      if ($WHATIFPREFERENCE) { continue }

      try {
        If ($text -ne $replace)
        {
            write-verbose "Writing '$tempname'."
        
            [IO.File]::WriteAllText("$tempname", $regex.Replace($text,
              $Replacement), [Text.Encoding]::$Encoding)
            write-verbose "Finished writing '$tempname'."
            write-verbose "Copying '$tempname' to '$file'."
            copy-item $tempname $file -force:$Force -erroraction Continue
            if ($?) {
              write-verbose "Finished copying '$tempname' to '$file'."
            }
        }
        else
        {
            Write-Verbose "File hadn't changed"
        }
        remove-item $tempname
        if ($?) {
          write-verbose "Removed file '$tempname'."
        }
      }
      catch [Management.Automation.MethodInvocationException] {
        write-error $ERROR[0]
      }
    } # foreach $file
  } # foreach $item
} # process

end { }