Unquoted strings about powershellpracticeandstyle HOT 3 OPEN

PowerShell/PowerShell#6467 tries to give a comprehensive overview of the current behavior with respect to arguments in command parsing mode - however, it doesn't cover the hashtable-key issue (see below).

about_Quoting_Rules is probably the best place to document this, though it is currently being discussed in the larger context of parsing modes in MicrosoftDocs/PowerShell-Docs#3440

As for use of unquoted key names in hash tables:

Without having looked at the source code, my understanding is as follows:

• If a key is a syntactically valid number literal, it is used as a number - including with suffixes such as u (U) for [uint32] and binary multiplier suffixes such as kb, as well as hex. numbers (e.g., 0x10) or numbers in exponential notation (e.g., 1e2 - , it is used as a number (this explains the 2U key turning into 2 of type System.UInt32 in your example).

• If a key starts with a digit, but is otherwise not a syntactically valid number literal, the hashtable definition fails.

  • Note: digit refers not just to the Latin decimal digits, but to all digits in the DecimalDigitNumber (Nd) Unicode category, which includes characters such as ๐ (THAI DIGIT ZERO, U+0E50)

• Otherwise, it is interpreted as a string, but parsing only succeeds if the token is limited to a sequence of the following characters (these seem to be the same that can be used in variable names without needing to enclose the name in {...} - see the about_Variables help topic's Variable Names that Include Special Characters section):

  • Characters from the following Unicode categories (defined in .NET as enumeration System.Globalization.UnicodeCategory the two-letter shorthands listed in parentheses can be used with \p{<shortCategoryName>} in regular expressions):

    • UppercaseLetter (Lu)
    • LowercaseLetter (Ll)
    • TitlecaseLetter (Lt)
    • ModifierLetter (Lm)
    • OtherLetter (Lo)
    • DecimalDigitNumber (Nd) - except as the first character (variable names don't have this restriction)

  • _ (underscore, the only allowed symbol)

To put it in terms of guidance:

Quote your hash-table keys, if:

• they should be strings but happen to start with a digit.

• they are strings that contain whitespace or a symbol other than _

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@mklement0, thank you for the comprehensive information, it is very helpful.

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It's worth pointing out that this same advice applies whenever you're interacting with a hashtable -- even when you're calling $hashtable.Add( or getting or setting via dot notation or indexing. I.e.:

$hashtable[2u] = "UInt"
$hashtable.2u

Also worth noting is that good syntax highlighting (such as at the prompt in PSReadline) will make the distinction really obvious:

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