Richard Siddaway's Blog

PowerShell enables you to work with the file system on your machine – one question that often comes up is how to create a directory.

When working interactively you can use md

PS> md c:\testf1


    Directory: C:\


 Mode                LastWriteTime         Length Name 
 ----                -------------         ------ ---- 
 d-----       19/08/2017     14:24                testf1

md doesn’t look like a PowerShell command – more like an old style DOS command.

Its actually an alias for mkdir

PS> Get-Command md

CommandType     Name                                               Version    Source 
 -----------     ----                                               -------    ------ 
 Alias           md –> mkdir

Which raises the question – what’s mkdir?

PS> Get-Command mkdir

CommandType     Name                                               Version    Source 
 -----------     ----                                               -------    ------ 
 Function        mkdir

Its a function that PowerShell creates for you

Digging into the function

PS> Get-ChildItem -Path function:\mkdir | select  -ExpandProperty  Definition

<# 
 .FORWARDHELPTARGETNAME New-Item 
 .FORWARDHELPCATEGORY Cmdlet 
 #>

[CmdletBinding(DefaultParameterSetName='pathSet', 
    SupportsShouldProcess=$true, 
    SupportsTransactions=$true, 
    ConfirmImpact='Medium')] 
    [OutputType([System.IO.DirectoryInfo])] 
param( 
    [Parameter(ParameterSetName='nameSet', Position=0, ValueFromPipelineByPropertyName=$true)] 
    [Parameter(ParameterSetName='pathSet', Mandatory=$true, Position=0, ValueFromPipelineByPropertyName=$true)] 
    [System.String[]] 
    ${Path},

    [Parameter(ParameterSetName='nameSet', Mandatory=$true, ValueFromPipelineByPropertyName=$true)] 
    [AllowNull()] 
    [AllowEmptyString()] 
    [System.String] 
    ${Name},

    [Parameter(ValueFromPipeline=$true, ValueFromPipelineByPropertyName=$true)] 
    [System.Object] 
    ${Value},

    [Switch] 
    ${Force},

    [Parameter(ValueFromPipelineByPropertyName=$true)] 
    [System.Management.Automation.PSCredential] 
    ${Credential} 
 )

begin {

    try { 
        $wrappedCmd = $ExecutionContext.InvokeCommand.GetCommand('New-Item', [System.Management.Automation.CommandTypes] 
 ::Cmdlet) 
        $scriptCmd = {& $wrappedCmd -Type Directory @PSBoundParameters } 
        $steppablePipeline = $scriptCmd.GetSteppablePipeline() 
        $steppablePipeline.Begin($PSCmdlet) 
    } catch { 
        throw 
    }

}

shows that its based on New-Item

PS> New-Item -Path c:\ -Name testf2 -ItemType Directory


    Directory: C:\


 Mode                LastWriteTime         Length Name 
 ----                -------------         ------ ---- 
 d-----       19/08/2017     14:32                testf2

The default for New-Item in the filesystem is to create a file so you need to use –ItemType Directory to create the folder.

If the folder you’re creating is a subfolder of a non-existent folder you can create the hierarchy is one go

PS> New-Item -Path c:\ -Name testf3\tests1 -ItemType Directory


    Directory: C:\testf3


 Mode                LastWriteTime         Length Name 
 ----                -------------         ------ ---- 
 d-----       19/08/2017     14:33                tests1


 PS> Get-ChildItem -Path c:\testf3 -Recurse


    Directory: C:\testf3


 Mode                LastWriteTime         Length Name 
 ----                -------------         ------ ---- 
 d-----       19/08/2017     14:33                tests1

This can get complicated if you try to nest too many levels so I recommend explicitly creating each level of your folder hierarchy. Its much easier to maintain and modify