When calling cmd script, comma in string is not preserved

[jiasli]

Steps to reproduce

Create a batch file mybatch.cmd containing:

@echo off
echo %1
echo %2

In PowerShell call it with

PS C:\Users\me> .\mybatch.cmd "a,b"
a
b
PS C:\Users\me> .\mybatch.cmd 'a,b'
a
b
PS C:\Users\me> .\mybatch.cmd --% "a,b"
"a,b"
ECHO is off.  # this is expected in cmd
PS C:\Users\me> .\mybatch.cmd --% 'a,b'
'a
b'            # this is expected in cmd

Expected behavior

Comma inside the string should be preserved, like when calling it in cmd:

mybatch.cmd "a,b"
"a,b"
ECHO is off.

Actual behavior

Comma is parsed as array.

Environment data

$PSVersionTable 

Name                           Value
----                           -----
PSVersion                      6.2.3
PSEdition                      Core
GitCommitId                    6.2.3
OS                             Microsoft Windows 10.0.18363
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

$PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.0.0-preview.6
PSEdition                      Core
GitCommitId                    7.0.0-preview.6
OS                             Microsoft Windows 10.0.18363
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

[mklement0]

It isn't PowerShell that parses the argument as an array, it is cmd that interprets unquoted token a,b as two arguments, because not only spaces but also , and ; can serve as argument separators.

PowerShell performs re-quoting as needed behind the scenes, and in the absence of spaces inside arguments, it currently decides that enclosing the value in double quotes is not necessary, so that both .\mybatch.cmd "a,b" and .\mybatch.cmd 'a,b' end up getting called as .\mybatch.cmd a,b, at which point cmd considers a and b separate arguments.

This re-quoting logic does not special-case calling cmd.exe or batch files, and is currently generally broken - see #1995

The workaround is to use embedded double quoting:

.\mybatch.cmd '"a,b"'
.\mybatch.cmd "`"a,b`""

You can use the iep function defined here to automate this quoting and to compensate for the other ways in which re-quoting is broken.

Note that the planned fix for #1995, detailed in this RFC, will break the workaround (as it will break all other current workarounds) and - unless cmd.exe / batch-file calls are special-cased - would offer no alternative (other than the limited --% approach) - see this comment.

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