Only One Join-Path Is Needed

Time to read: ~ 3 minutes

Words: 571

Update: Learning from my mistakes aka Failing Up

Update: Reliably informed that `-AdditionalChildPath` was added after 5.1

Join Me For a Moment

There’s a multitude of scripts out in the wild with a chain of Join-Path commands. Initially, when I wanted to create a path safely, a Join-Path cmdlets chain was also my go-to. However, after reading up on the documentation, I realised another way: I only need a singular instance of the Join-Path command.

Target Location

My PowerShell console is open in my home folder, and I’ve a test file: /home/soneill/PowerShell/pester-5-groupings/00-run-tests.ps1.

If I wanted to create a variable that goes to the location of that file, one of the safe ways of doing that is to use Join-Path.

Long Form

I mean, I could create the variable myself by concatenating strings, but then I’d have to take the path separator into account depending if I’m on Windows or not.

Apparently not…

$var = ".\PowerShell\pester-5-groupings\00-run-tests.ps1"

[PSCustomObject] @{
  Type      = 'Long Form'
  Separator = 'Manual entry: \'
  Variable  = $var
  Path      = try {Get-ChildItem -Path $var -ErrorAction Stop} catch {'Error!'}
}

I thought this wouldn’t work but, when running the code samples, it appears that PowerShell doesn’t mind me using a forward-slash (/) or a back-slash (\); it’ll take care of the proper separator for me.

UPDATE: This way works fine from a file but run the script from a PowerShell terminal and it’s a no-go.

UPDATED UPDATE: Thanks for Cory Knox (twitter) and Steven Judd (twitter) for pointing out that this fails because it’s using /bin/ls instead of the Get-ChildItem alias:

Manual Creation

A more explicit, cross-platform method would be to use the [IO.Path]::DirectorySeparatorChar.

$sep = [IO.Path]::DirectorySeparatorChar
$var = ".${sep}PowerShell${sep}pester-5-groupings${sep}00-run-tests.ps1"

[PSCustomObject] @{
  Type      = 'Manual Creation'
  Separator = "[IO.Path]::DirectorySepartorChar: $sep"
  Variable  = $var
  Path      = try {Get-ChildItem -Path $var -ErrorAction Stop} catch {'Error!'}
}

This method works fine but creating the path can get very long if I don’t use a variable. Even using a variable, I have to wrap the name in curly braces because of the string expansion method I used. That’s not something that I would expect someone picking up PowerShell for the first time to know.

-f Strings

In case you’re wondering, another string expansion method here would be to use -f strings.

$sep = [IO.Path]::DirectorySeparatorChar
$varf = '.{0}PowerShell{0}pester-5-groupings{0}00-run-tests.ps1' -f $sep

[PSCustomObject] @{
  Type = 'F String'
  Separator = "[IO.Path]::DirectorySepartorChar: $sep"
  Variable  = $varf
  Path      = try {Get-ChildItem -Path $varf -ErrorAction Stop} catch {'Error!'}
}

Many Join-Path Commands

Better yet would be if I didn’t have to account for the separator at all. Here’s where the multiple Join-Path cmdlets come into play.

$var2 = Join-Path -Path . -ChildPath PowerShell | Join-Path -ChildPath pester-5-groupings | Join-Path -ChildPath 00-run-tests.ps1
 
[PSCustomObject] @{
  Type      = 'Many join paths'
  Separator = 'Taken care of: Join-Path'
  Variable  = $var2
  Path      = try {Get-ChildItem -Path $var2 -ErrorAction Stop} catch {'Error!'}
}

Multiple Join-Path commands work fine. No real issue with people using this way, but there is another!

Only One Join-Path Needed

Join-Path has a parameter called -AdditionalChildPath that takes the remaining arguments from the command line and uses them in much the same way as a Join-Path command chain would.

$var3 = Join-Path -Path . -ChildPath PowerShell -AdditionalChildPath 'pester-5-groupings', '00-run-tests.ps1'

[PSCustomObject] @{
  Type = 'AdditionalChildPaths'
  Separator = 'Taken care of: Join-Path'
  Variable = $var3
  Path = try {Get-ChildItem -Path $var3 -ErrorAction Stop} catch {'Error!'}
}

More Output than Put Out

So there you go—more than one way to join a path. Use whichever ones work for you. It’s good to know your options, though.