Parameter parsing/passing: an unquoted argument that starts with a "-" (hyphen) is broken in two at the first "." (period)

^{Related: #6292 and #6360}

Note that . should receive no special treatment in tokens such as -foo=bar.baz, because the token is unquoted and does not start with a special char. ($ @ ( ' " ) and should therefore result in interpretation as an (expandable) string, according to about_Parsing.

In reality, though, the unexpected special treatment stems from - being the 1st character, which causes interpretation as a parameter name, even though that doesn't apply in this case.

Steps to reproduce

# Helper function that echoes all arguments.
function Out-Argument { $i = 0; $Args | % { 'arg[{0}]: {1}' -f $i++, $_ } }

# Pass an unquoted argument that starts with "-" and has an embedded "." (outside of "..." or '...')
Out-Argument -foo=bar.baz

Expected behavior

arg[0]: -foo=bar.baz

Actual behavior

arg[0]: -foo=bar
arg[1]: .baz

The token was unexpectedly broken in two. Note that this equally applies when calling external utilities.

And it is indeed in the context of calling external programs that an argument with such (non-PowerShell) syntax (-<param-name>=<value>) may need to be passed - see this SO question and this one.

(PSv2 exhibited a variation of the bug - see this SO question.)

Environment data

PowerShell Core v6.0.1 on macOS 10.13.3
PowerShell Core v6.0.1 on Ubuntu 16.04.3 LTS
PowerShell Core v6.0.1 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)
Windows PowerShell v5.1.15063.674 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)

Workarounds

# "`"-escape the leading "-"
Out-Argument `-foo=bar.baz

# Quote the whole argument
Out-Argument '-foo=bar.baz'

Garrett hit this trying to use cmake with pwsh: https://twitter.com/fearthecowboy/status/1336758436583809026

Twitter
Garrett Serack🤠 on Twitter
“I just wandered across the absolute weirdest bug in powershell & pwsh
When using a parameter that starts with a dash, powershell will insert a space before a period in the command line:

This is bad when trying to execute a program (example here with cmd /c echo)

@Steve_MSFT”

Steve Lee (@SteveL-MSFT)

Just to clarify, Steve Lee (@SteveL-MSFT): it isn't that a space is inserted - that's just how it manifests in a test command such as cmd /c echo -foo=bar.none; what happens is that the part of the argument starting with the (first) . is passed as a separate argument.

#14364 should be closed as a duplicate.

Work around PowerShell/PowerShell#6291

@PowerShell/powershell-committee reviewed this, we believe the treatment of the period as an argument separator is a bug that should be fixed. A bucket 3 breaking change.

Steve Lee (@SteveL-MSFT)

Glad to hear it, Steve Lee (@SteveL-MSFT).

I hope that fixing this will also address #6292 and #6360.

_content/doc: fix go mod edit for PowerShell

Is this still on track for 7.2?

I can't use Powershell for my project because of this.

Here's a real example for usage of the period in arguments. File names usually have periods.

clang++ -std=c++20 use.cpp -fmodule-file=Hello=Hello.pcm Hello.pcm -o Hello.out

The command was taken from https://clang.llvm.org/docs/StandardCPlusPlusModules.html.

Standard C++ Modules — Clang 19.0.0git documentation

This has been an issue for a long time. I see it on version 5 and on version 7.

I can see five characters that are allowed in Unix shell unquoted strings that aren't allowed in PowerShell:

{
}
,
.
[

In the file src/System.Management.Automation/engine/parser/tokenizer.cs, if I remove case '.': from line 3211, then this problem is fixed. However, it probably breaks some other functionality.

Before change:

PS C:\> echo -Hello.world
-Hello
.world

After change:

PS C:\> echo -Hello.world    
-Hello.world

WG-Engine looked at this today and agree it is worth pursuing a bug fix for native commands. Attempting to fix this for commands in general, would be too risky. This area of the code is tricky because the native command parser only gets the tokens that made up the command line, but we believe the original argument can be recreated from these tokens.

Fix hyphen-prefixed arguments being split at period

Fix Azure VM Windows test flags splitting on dotted build IDs (#774)

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Parameter parsing/passing: an unquoted argument that starts with a "-" (hyphen) is broken in two at the first "." (period) #6291

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Parameter parsing/passing: an unquoted argument that starts with a "-" (hyphen) is broken in two at the first "." (period) #6291

Description

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SteveL-MSFT commented on Dec 10, 2020

mklement0 commented on Dec 10, 2020

SteveL-MSFT commented on Dec 16, 2020

mklement0 commented on Dec 16, 2020

ceztko commented on Oct 6, 2021

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