Why is $false -eq “” true?

by

When doing comparison operations, PowerShell will automatically attempt to coerce the object on the right-hand side of the operator to match the type on the left-hand side.

In the case of coercing [string] to [bool], any non-null string will evaluate as $true, and a null string will evaluate as $false. See blog post Boolean Values and Operators for more information about automatic conversion of different data types to boolean values.

This sometimes leads to unexpected results:

PS C:\> [bool]"$false" 

True

The string value of $false is ‘False’, which is a non-null string and evaluated to $true when cast back to [bool].

It also makes comparison operations non-commutative when the operands are of different data types:

PS C:\> '' -eq $false
False
PS C:\> $false -eq ''
True

In the first comparison the value $false is auto-cast to a string in order to match the type of the first operand (''), so you’re actually comparing '' -eq 'False', which evaluates to $false.

In the second comparison the string '' is auto-cast to a boolean, again in order to match the type of the first operand ($false), so this time you’re actually comparing $false -eq $false, which evaluates to $true.

More Related Contents:

  1. What’s the best way to determine the location of the current PowerShell script?
  2. Powershell Invoke-WebRequest Fails with SSL/TLS Secure Channel
  3. How can I find the Upgrade Code for an installed MSI file?
  4. How to enter a multi-line command
  5. Add a where-object on a table construct?
  6. Is there a way to make a PowerShell script work by double clicking a .ps1 file?
  7. How to redirect the output of a PowerShell to a file during its execution
  8. How can I make PowerShell handle [ or ] in file name well?
  9. What’s the difference between .replace and -replace in powershell?
  10. Get remote registry value
  11. Why does the `using` scope work locally with Start-Job, but not Invoke-Command?
  12. Catching FULL exception message
  13. Get-Content and show control characters such as `r – visualize control characters in strings
  14. Powershell send-mailmessage – email to multiple recipients
  15. Replacing only the first occurrence of a word in a string
  16. Function Get-IniContent is not recognized – INI file support inPowerShell
  17. How can I get the current PowerShell executing file?
  18. What’s the equivalent of xargs in PowerShell?
  19. Visual studio code cmd error: Cannot be loaded because running scripts is disabled on this system
  20. Copy file remotely with PowerShell
  21. Invoke-WebRequest, POST with parameters
  22. What does the & symbol in powershell mean?
  23. Powershell Get-ChildItem -Filter operates differently to Where clause with same value
  24. Can’t install nuget package because of “Failed to initialize the PowerShell host”
  25. What security setting is preventing Remote PowerShell 2.0 from accessing UNC paths
  26. PowerShell Capture Write-Host output
  27. start remote process within the context
  28. How can I elevate Powershell while keeping the current working directory AND maintain all parameters passed to the script?
  29. Are you able to use PtrToStringAuto to decrypt a secure string in Powershell 7 on macOS?
  30. Prevent trailing newline in PowerShell Out-File command

Leave a Comment