Can't run icacls to a directory with spaces

To add an explanation to your own effective workaround (not including a trailing \ in your argument):

What you're seeing is a bug in Windows PowerShell with respect to how it passes arguments to external programs - this problem has been fixed in PowerShell (Core) 7.

Behind the scenes, PowerShell (of necessity) translates your single-quoted argument containing spaces to a double-quoted form, because external CLIs can only be assumed to understand "..." quoting.

The command-line parsing rules used by most CLIs consider the sequence \" to be an escaped " character, i.e. a " character to be considered a verbatim part of the argument rather than delimiting it.

Therefore, a verbatim \ at the end of a double-quoted string must itself be escaped as \\ in order to be recognized as such - this is what Windows PowerShell neglects to do:

That is, Windows PowerShell translates your call as follows:

# Resulting command line as used behind the scenes for actual invocation.
# WinPS: BROKEN, because the \ at the end isn't escaped.
icacls.exe ".\My Digital Editions\"

When icacls.exe parses this command line, it sees verbatim .\My Digital Editions" (note the verbatim " at the end), as reflected in the error message.

PowerShell (Core) 7, by contrast, does perform the necessary escaping:

# Resulting command line as used behind the scenes for actual invocation.
# PowerShell (Core): OK
icacls.exe ".\My Digital Editions\\"

Workarounds:

• In a literal path, simply omit a trailing \ - which won't work for a root path, however, and it also assumes that this doesn't change the meaning of the argument from the target program's perspective (it doesn't for icacls.exe).

  • Programmatic solution:

    $path = '.\My Digital Editions\'
    icacls.exe $path.TrimEnd('\')  # !! Doesn't work for ROOT paths, e.g. "C:\"
    

• Alternatively - which also works for root paths - manually double the trailing \

  • Quick-and-dirty programmatic solution, knowing that file-system paths may contain duplicated \ separators without ill-effects (however, it may affect path comparisons):

    icacls.exe "$path\"
    

• A robust, cross-edition programmatic solution that doesn't modify the argument is a bit more cumbersome:

  icacls.exe $(if ($path.EndsWith('\') -and $PSVersionTable.PSEdition -ne 'Core') { "$path\" } else { $path })
  

As an aside:

A related bug that affects how " (double quotes) embedded in arguments are passed to external programs affects PowerShell (Core) 7 up to v7.2.x - see this answer.