PowerShell: Set-Content having issues with "file already in use"

Question

I'm working on a PowerShell script that finds all the files with PATTERN within a given DIRECTORY, prints out the relevant lines of the document with the PATTERN highlighted, and then replaces the PATTERN with a provided REPLACE word, then saves the file back. So it actually edits the file.

Except I can't get it to alter the file, because Windows complains about the file already being open. I tried several methods to solve this, but keep running into the issue. Perhaps someone can help:

param(
    [string] $pattern = ""
    ,[string] $replace = ""
    ,[string] $directory ="."
    ,[switch] $recurse = $false
    ,[switch] $caseSensitive = $false)

if($pattern -eq $null -or $pattern -eq "")
{
    Write-Error "Please provide a search pattern." ; return
}

if($directory -eq $null -or $directory -eq "")
{
    Write-Error "Please provide a directory." ; return
}

if($replace -eq $null -or $replace -eq "")
{
    Write-Error "Please provide a string to replace." ; return
}

$regexPattern = $pattern
if($caseSensitive -eq $false) { $regexPattern = "(?i)$regexPattern" }
$regex = New-Object System.Text.RegularExpressions.Regex $regexPattern

function Write-HostAndHighlightPattern([string] $inputText)
{
    $index = 0
    $length = $inputText.Length
    while($index -lt $length)
    {
        $match = $regex.Match($inputText, $index)
        if($match.Success -and $match.Length -gt 0)
        {
            Write-Host $inputText.SubString($index, $match.Index) -nonewline
            Write-Host $match.Value.ToString() -ForegroundColor Red -nonewline
            $index = $match.Index + $match.Length
        }
        else
        {
            Write-Host $inputText.SubString($index) -nonewline
            $index = $inputText.Length
        }
    }
}

Get-ChildItem $directory -recurse:$recurse |
    Select-String -caseSensitive:$caseSensitive -pattern:$pattern |    
    foreach {
        $file = ($directory + $_.FileName)
        Write-Host "$($_.FileName)($($_.LineNumber)): " -nonewline
        Write-HostAndHighlightPattern $_.Line
        %{ Set-Content $file ((Get-Content $file) -replace ([Regex]::Escape("[$pattern]")),"[$replace]")}
        Write-Host "`n"
        Write-Host "Processed: $($file)"
    }

The issue is located within the final block of code, right at the Get-ChildItem call. Of course, some of the code in that block is now a bit mangled due to me trying to fix the problem then stopping, but keep in mind the intent of that part of the script. I want to get the content, replace the words, then save the altered text back to the file I got it from.

Any help at all would be greatly appreciated.

Answer 1

Removed my previous answer, replacing it with this:

Get-ChildItem $directory -recurse:$recurse
foreach {        
    $file = ($directory + $_.FileName)

    (Get-Content $file) | Foreach-object {
        $_ -replace ([Regex]::Escape("[$pattern]")),"[$replace]")
    } | Set-Content $file
}

Note:

• The parentheses around Get-Content to ensure the file is slurped in one go (and therefore closed).
• The piping to subsequent commands rather than inlining.
• Some of your commands have been removed to ensure it's a simple test.