I'm using a program that takes as one of its parameters a string that will be
appended to the output. One possible option for this parameter is the empty
string. I can pass the empty string from a cmd.exe shell with "".

For example, consider the Visual Basic script, named print-args.vbs:
WScript.echo WScript.Arguments.Item(0)
WScript.echo WScript.Arguments.Item(1)
WScript.echo Wscript.Arguments.Item(2)

If this script is executed using the following syntax:

PS C:\> cmd /c 'cscript /Nologo print-args.vbs foo "" bar'

foo

bar

But if the same script is run from the Powershell, the parameter is missing.

PS C:\> cscript /Nologo print-args.vbs foo "" bar
foo
bar
C:\print-args.vbs(3, 1) Microsoft VBScript runtime error: Subscript out of
range

After some muddling around with the syntax, I found that I could in fact
force Powershell to pass the empty string using the following syntax.

PS C:\> cscript /Nologo print-args.vbs foo `"`" bar
foo

bar

So for my question.

Is the `"`" the recommended syntax for passing an empty-string parameter?

I find the syntax confusing... and in the case of my application, when I use
the "" syntax that works in cmd.exe and other common shells (i.e. bash), it's
silently ignored by Powershell, so the subsequent parameter gets consumed
where I intended to have an empty string. This causes very bad unintended
behavior.

I acknowledge that Powershell isn't cmd.exe or bash, but I have another
question. Is there a reason that "" or '' couldn't be honored as the empty
string when passed to a child command? If the answer is no, I'll follow up
with a ticket on MS Connect.



Regards,
Jason

Hi Jason,

Can you try this:


cscript /Nologo print-args.vbs foo '""' bar

- or -

cscript /Nologo print-args.vbs foo ([string]::empty) bar






---
Shay Levy
Windows PowerShell MVP
http://blogs.microsoft.co.il/blogs/ScriptFanatic
PowerShell Toolbar: http://tinyurl.com/PSToolbar



JC> I'm using a program that takes as one of its parameters a string
JC> that will be appended to the output. One possible option for this
JC> parameter is the empty string. I can pass the empty string from a
JC> cmd.exe shell with "".
JC>
JC> For example, consider the Visual Basic script, named print-args.vbs:
JC> WScript.echo WScript.Arguments.Item(0)
JC> WScript.echo WScript.Arguments.Item(1)
JC> WScript.echo Wscript.Arguments.Item(2)
JC> If this script is executed using the following syntax:
JC>
JC> PS C:\> cmd /c 'cscript /Nologo print-args.vbs foo "" bar'
JC>
JC> foo
JC>
JC> bar
JC>
JC> But if the same script is run from the Powershell, the parameter is
JC> missing.
JC>
JC> PS C:\> cscript /Nologo print-args.vbs foo "" bar
JC> foo
JC> bar
JC> C:\print-args.vbs(3, 1) Microsoft VBScript runtime error: Subscript
JC> out of
JC> range
JC> After some muddling around with the syntax, I found that I could in
JC> fact force Powershell to pass the empty string using the following
JC> syntax.
JC>
JC> PS C:\> cscript /Nologo print-args.vbs foo `"`" bar foo
JC>
JC> bar
JC>
JC> So for my question.
JC>
JC> Is the `"`" the recommended syntax for passing an empty-string
JC> parameter?
JC>
JC> I find the syntax confusing... and in the case of my application,
JC> when I use the "" syntax that works in cmd.exe and other common
JC> shells (i.e. bash), it's silently ignored by Powershell, so the
JC> subsequent parameter gets consumed where I intended to have an empty
JC> string. This causes very bad unintended behavior.
JC>
JC> I acknowledge that Powershell isn't cmd.exe or bash, but I have
JC> another question. Is there a reason that "" or '' couldn't be
JC> honored as the empty string when passed to a child command? If the
JC> answer is no, I'll follow up with a ticket on MS Connect.
JC>
JC> Regards,
JC> Jason

The problem is that you don't need an empty string, you SPECIFICALLY
need a pair of quotes, which cscript will PARSE as an empty string.

PowerShell converts the "" to an empty string, and as far as cscript is
concerned, that just means that foo "" bar = foo bar

So, you'll get the same results if you do this:

cscript /nologo print-args.vbs foo '""' bar

or this ...

cscript /nologo print-args.vbs foo """""" bar

or this

cscript /nologo print-args.vbs foo "`"`"" bar

or even this ...

$empty = '""'
cscript /nologo print-args.vbs foo $empty bar


.... basically, anything that generates a STRING which consists of a pair
of quotes ...


--
Joel

Jason R. Coombs wrote:

> I'm using a program that takes as one of its parameters a string that will be
> appended to the output. One possible option for this parameter is the empty
> string. I can pass the empty string from a cmd.exe shell with "".
>
> For example, consider the Visual Basic script, named print-args.vbs:
> WScript.echo WScript.Arguments.Item(0)
> WScript.echo WScript.Arguments.Item(1)
> WScript.echo Wscript.Arguments.Item(2)
>
> If this script is executed using the following syntax:
>
> PS C:\> cmd /c 'cscript /Nologo print-args.vbs foo "" bar'
>
> foo
>
> bar
>
> But if the same script is run from the Powershell, the parameter is missing.
>
> PS C:\> cscript /Nologo print-args.vbs foo "" bar
> foo
> bar
> C:\print-args.vbs(3, 1) Microsoft VBScript runtime error: Subscript out of
> range
>
> After some muddling around with the syntax, I found that I could in fact
> force Powershell to pass the empty string using the following syntax.
>
> PS C:\> cscript /Nologo print-args.vbs foo `"`" bar
> foo
>
> bar
>
> So for my question.
>
> Is the `"`" the recommended syntax for passing an empty-string parameter?
>
> I find the syntax confusing... and in the case of my application, when I use
> the "" syntax that works in cmd.exe and other common shells (i.e. bash), it's
> silently ignored by Powershell, so the subsequent parameter gets consumed
> where I intended to have an empty string. This causes very bad unintended
> behavior.
>
> I acknowledge that Powershell isn't cmd.exe or bash, but I have another
> question. Is there a reason that "" or '' couldn't be honored as the empty
> string when passed to a child command? If the answer is no, I'll follow up
> with a ticket on MS Connect.
>
> Regards,
> Jason