I’m putting together a list of common “gotchas” for PowerShell, mainly things that affect newcomers. So far, I’ve got:

• Piping the output of a Format cmdlet to nearly anything else
• Using -contains instead of -like
• Selecting a subset of object properties and then trying to sort/fiter on a now-missing property
• Wrong syntax for -filter parameters on various commands
• Commands that don’t produce pipeline output (e.g., piping Export-CSV to something)
• Using ConvertTo-HTML without -Fragment and appending multiple pages in one file
• Confusion with ( [ { and the other punctuation
• Concatenating strings (hard) vs. using double quotes (easier)
• $ not being part of the variable name (esp with -ErrorVariable)
• Accumulating objects in a variable and returning it, vs. outputting to the pipeline directly

What are your “gotchas?”