Backup Docker named volumes (Docker for Windows)

backup.ps1

param (
    [Parameter(Mandatory = $true, HelpMessage = "List all named volumes you want to backup. <volume1,volume2,volume3>")]
    [string[]] $Volumes,
    [Parameter(Mandatory = $true, HelpMessage = "Backup path")]
    [string] $Path
)

$ErrorActionPreference = "Stop"

"Checking volumes..."
foreach ($volume in $Volumes) {
    $out = ""
    Invoke-Expression "docker ps -q -f 'volume=${volume}'" | Tee-Object -Variable out > $null
    $lines = $out | Measure-Object -Line
    $count = $lines.Count

    if (($count -gt 0) -and ($lines[0].Lines -gt 0)) {
        "Volume ${volume} is currenty in use by ${count} container(s) (${out}). First stop this container and then try again."
        "Exiting..."
        exit 1
    }
}

"Preparing..."
$dockerRun = "docker run --rm -it -d "
foreach ($volume in $Volumes) {
    $dockerRun += "-v ${volume}:/backup/${volume}:ro "
}
$dockerRun += "--name backup alpine"
Invoke-Expression $dockerRun > $null
Invoke-Expression "docker exec backup apk add zip" > $null

foreach ($volume in $Volumes) {
    "Copying ${volume}..."

    Invoke-Expression "docker exec -w /backup/${volume} backup zip -r /tmp/${volume}.zip ." > $null
    # TODO add hash value to archive name
    # Invoke-Expression "docker exec backup mv /tmp/${volume}.zip ""/tmp/${volume}-`sha1sum /tmp/tk-utrip-wp.zip | awk '{print `$1;}'`.zip"""
    Invoke-Expression "docker cp backup:/tmp/${volume}.zip $(Join-Path -Path $Path -ChildPath $volume).zip" > $null
}

"Cleaning up..."
Invoke-Expression "docker kill backup" > $null

example.txt

# Backup Docker named volumes (Docker for Windows)
Backup named volumes (hosted inside MobyLinuxVM) to host machine.

### Find volumn names
```
docker volume ls
```

### Usage example
```
mkdir .\backup\20190210
.\backup.ps1 -Volumes volum-name-1,volume-name-2 -Path .\backup\20190210
```