Start-Process with PowerShell.exe exhibits different behavior with embedded single quotes and double quotes

by

js2010’s helpful answer is correct in that the use of Start-Process is incidental to your question and that the behavior is specific to PowerShell’s CLI (powershell.exe for Windows PowerShell, and pwsh for PowerShell (Core) 6+):

On Windows[1], there are two layers of evaluation to consider:

  • (a) The initial parsing of the command line into arguments.

  • (b) The subsequent evaluation of the resulting arguments following the -Command (-c) CLI parameter as PowerShell code.

    • Note: In Windows PowerShell CLI calls, -Command is implied if neither -Command nor -File are specified; in PowerShell (Core), -File is the default.

Re (a):

As most console programs on Windows do, PowerShell recognizes only " chars. (double quotes) – not also ' (single quotes) – as having syntactic function.[2]

  • That is, unless " chars. are escaped as \", they are treated as command-line argument delimiters with purely syntactic function, which are therefore removed during parsing.

    • A quick example: powershell -c "hi!" makes PowerShell strip the " and try to execute hi! as a command; by contrast, powershell -c \"hi!\" escapes and therefore retains the " as part of the command, so that PowerShell executes "hi!", i.e. a string literal that is echoed as such.

    • Note: If you’re calling from cmd.exe, \" escape sequences can situationally break the invocation; for robust workarounds see this answer.

  • As implied by the above, ' chars. are not removed.

Re (b)

Whatever arguments are the result – an array of possibly "-stripped tokens – are concatenated with a single space between them, and the resulting (single) string is then interpreted as PowerShell code.

To explain this in the context of your example, with Start-Process taken out of the picture:

Note: The following applies to calling from cmd.exe or any context where no shell is involved (including Start-Process and the Windows Run (WinKey-R) dialog). By contrast, PowerShell re-quotes the command line behind the scenes to always use ", if needed.
To put it differently: the following applies to command lines as seen by PowerShell.

Single-quoted command:

# Note: This *would* work for calling ping if run from 
#       (a) PowerShell itself or (b) from a POSIX-like shell such as Bash.
#       However, via cmd.exe or any context where *no* shell is involved,
#       notably Start-Process and the Windows Run dialog, it does not.
powershell -Command 'ping google.com'

  • (a) results in PowerShell finding the following two verbatim arguments: 'ping and google.com'

  • (b) concatenates these verbatim arguments to form 'ping google.com'[2] and executes that as PowerShell code, therefore outputs the content of this string literal, ping google.com

Double-quoted command:

powershell -Command "ping google.com"

  • (a) results in PowerShell stripping the syntactic " characters, finding the following, single verbatim argument: ping google.com

  • (b) then results in this verbatim argument – ping google.com – being executed as PowerShell code, which therefore results in a command invocation, namely of the ping executable with argument google.com.

[1] On Unix-like platforms, the first layer doesn’t apply, because programs being invoked only ever see an array of verbatim arguments, not a command line that they themselves must parse into arguments. Not that if you call the PowerShell CLI from a POSIX-like shell such as bash on Unix-like platforms, it is that shell that recognizes single-quotes as string delimiters, and strips them before PowerShell sees them.

[2] Surprisingly, on Windows it is ultimately up to each individual program to interpret the command line, and some do choose to also recognize ' as string delimiters (e.g., Ruby). However, many programs on Windows – including PowerShell itself – are based on the C runtime, which only recognizes ".

[3] As an aside, note that this implies that whitespace normalization is taking place: that is,
powershell -Command 'ping google.com' would equally result in 'ping google.com'.

More Related Contents:

  1. How do I call the PowerShell CLI robustly, with respect to character encoding, input and output streams, quoting and escaping?
  2. Powershell: passing json string to curl
  3. Using a Variable (PowerShell) inside of a command
  4. ‘kubectl patch’ works on Linux Bash but not in Windows Powershell ISE
  5. Escaping the and (&) sign in Powershell
  6. Powershell Formatting for a String
  7. dotnet ef scaffold Unrecognized option ‘-t firstTable -t secondTable’ – pass arguments stored in a string
  8. How to delete subfolders and Files but not parent Folder in windows using Script? [closed]
  9. Execute PowerShell Script from C# with Commandline Arguments
  10. Using PowerShell credentials without being prompted for a password
  11. PowerShell and the -contains operator
  12. Powershell function call changing passed string into int
  13. Different behaviour and output when piping in CMD and PowerShell
  14. PowerShell’s parsing modes: argument (command) mode vs. expression mode
  15. How do I capture the output into a variable from an external process in PowerShell?
  16. Character-encoding problem with string literal in source code
  17. How to handle failed variable assignments in powershell? [duplicate]
  18. Redirecting standard input\output in Windows PowerShell
  19. How to perform keystroke inside powershell?
  20. How to get an object’s property’s value by property name?
  21. Delete files older than 15 days using PowerShell
  22. Reload the path in PowerShell
  23. Powershell equivalent of bash ampersand (&) for forking/running background processes
  24. Why does ‘continue’ behave like ‘break’ in a Foreach-Object?
  25. Why don’t .NET objects in PowerShell use the current directory?
  26. Timing a command’s execution in PowerShell
  27. Write-Host vs Write-Information in PowerShell 5
  28. How remove accents in PowerShell?
  29. How to split long commands over multiple lines in PowerShell
  30. Is there a powershell pattern for if($?) { }

Leave a Comment