Powershell function to replace or add lines in text files

Question

I'm working on a powershell script that modifies config files. I have files like this:

#####################################################
# comment about logentrytimeout
#####################################################
Logentrytimeout= 1800

who should look like this:

#####################################################
# comment about logentrytimeout
#####################################################
Logentrytimeout= 180
disablepostprocessing = 1
segmentstarttimeout = 180

If there is a key set(Logentrytimeout), just update it to the given value. Ignore comments, where the key is mentioned(lines that start with #). The Key is case insensitive.

If the key is not set(disablepostprocessing and segmentstarttimeout), append key and value to the file. My function so far goes like this:

function setConfig( $file, $key, $value )
{
  (Get-Content $file) |
  Foreach-Object {$_ -replace "^"+$key+".=.+$", $key + " = " + $value } |
  Set-Content $file
}

setConfig divider.conf "Logentrytimeout" "180"
setConfig divider.conf "disablepostprocessing" "1"
setConfig divider.conf "segmentstarttimeout" "180"

• What is the correct regex?
• How do I check if there was a replacement?
• If there was no replacement: How can I append $key+" = "+$value to the file then?

Answer 1

Assuming the $key you want to replace is always at the beginning of a line, and that it contains no special regex characters

function setConfig( $file, $key, $value ) {
    $content = Get-Content $file
    if ( $content -match "^$key\s*=" ) {
        $content -replace "^$key\s*=.*", "$key = $value" |
        Set-Content $file     
    } else {
        Add-Content $file "$key = $value"
    }
}

setConfig "divider.conf" "Logentrytimeout" "180" 

If there is no replacement $key = $value will be appended to the file.

Answer 2

Updated version of the functions above with some parametrisation and verbose output if required.

   Function Set-FileConfigurationValue()
{
    [CmdletBinding(PositionalBinding=$false)]   
    param(
        [Parameter(Mandatory)][string][ValidateScript({Test-Path $_})] $Path,
        [Parameter(Mandatory)][string][ValidateNotNullOrEmpty()] $Key,
        [Parameter(Mandatory)][string][ValidateNotNullOrEmpty()] $Value,
        [Switch] $ReplaceExistingValue,
        [Switch] $ReplaceOnly
    )

    $content = Get-Content -Path $Path
    $regreplace = $("(?<=$Key).*?=.*")
    $regValue = $("=" + $Value)
    if (([regex]::Match((Get-Content $Path),$regreplace)).success)
    {
        If ($ReplaceExistingValue)
        {
            Write-Verbose "Replacing configuration Key ""$Key"" in configuration file ""$Path"" with Value ""$Value"""
            (Get-Content -Path $Path) | Foreach-Object { [regex]::Replace($_,$regreplace,$regvalue) } | Set-Content $Path
        }
        else
        {
            Write-Warning "Key ""$Key"" found in configuration file ""$Path"". To replace this Value specify parameter ""ReplaceExistingValue"""
        }
    } 
    elseif (-not $ReplaceOnly) 
    {    
        Write-Verbose "Adding configuration Key ""$Key"" to configuration file ""$Path"" using Value ""$Value"""
        Add-Content -Path $Path -Value $("`n" + $Key + "=" + $Value)       
    }
    else
    {
        Write-Warning "Key ""$Key"" not found in configuration file ""$Path"" and parameter ""ReplaceOnly"" has been specified therefore no work done"
    }
}