Watch file for changes and run command with powershell

Question

Is there any simple way(i.e., script) to watch file in Powershell and run commands if file changes. I have been googling but can't find simple solution. Basically I run script in Powershell and if file changes then Powershell run other commands.

EDIT

Ok I think I made a mistake. I don't need script, a need function that I can include in my $PROFILE.ps1 file. But still, I was trying hard and still I'm unable to write it, so I will give bounty. It have to look like this:

function watch($command, $file) {
  if($file #changed) {
    #run $command
  }
}

There is a NPM module that is doing what I want, watch , but it only watches for folders not files, and it's not Powershell xD.

Answer 1

I will add another answer, because my previous one did miss the requirements.

Requirements

• Write a function to WAIT for a change in a specific file
• When a change is detected the function will execute a predefined command and return execution to the main script
• File path and command are passed to the function as parameters

There is already an answer using file hashes. I want to follow my previous answer and show you how this can be accomplish using FileSystemWatcher.

$File = "C:\temp\log.txt"
$Action = 'Write-Output "The watched file was changed"'
$global:FileChanged = $false

function Wait-FileChange {
    param(
        [string]$File,
        [string]$Action
    )
    $FilePath = Split-Path $File -Parent
    $FileName = Split-Path $File -Leaf
    $ScriptBlock = [scriptblock]::Create($Action)

    $Watcher = New-Object IO.FileSystemWatcher $FilePath, $FileName -Property @{ 
        IncludeSubdirectories = $false
        EnableRaisingEvents = $true
    }
    $onChange = Register-ObjectEvent $Watcher Changed -Action {$global:FileChanged = $true}

    while ($global:FileChanged -eq $false){
        Start-Sleep -Milliseconds 100
    }

    & $ScriptBlock 
    Unregister-Event -SubscriptionId $onChange.Id
}

Wait-FileChange -File $File -Action $Action