Hello,

If Tcl's "exec" command is used to execute a command, how does one see
the exact command that is issued to the OS?

I'm asking this question because I'm investigating the failure of
statements such as:

set someDir C:[file nativename /Users]
exec -- cmd.exe /C cd $someDir && dir

which responds: "The system cannot find the path specified."

If I disable command extensions:

exec -- cmd.exe /E:OFF /C cd $someDir && dir

I don't get an error but I don't get the expected list of files either.

However, this command works as expected:

exec -- cmd.exe /C dir $someDir

so I'm thinking it has something to do with the &&, hence my question.

One more thing. Such commands did work a few months ago so something
has changed.

I see this on Windows 10 using both Tcl 8.6.9 and 8.6.12.

Thanks in advance for any help/insights.

-mike

On 05/31/2022 1:08 PM, Michael Soyka wrote:
> Hello,
>
> If Tcl's "exec" command is used to execute a command, how does one see
> the exact command that is issued to the OS?
>
> I'm asking this question because I'm investigating the failure of
> statements such as:
>
>     set someDir C:[file nativename /Users]
>     exec -- cmd.exe /C cd $someDir && dir
>
> which responds: "The system cannot find the path specified."

However, this alternative does work:

exec -- cmd.exe /C "cd $someDir && dir"

but I don't understand why.

>
> If I disable command extensions:
>
>     exec -- cmd.exe /E:OFF /C cd $someDir && dir
>
> I don't get an error but I don't get the expected list of files either.
>
> However, this command works as expected:
>
>     exec -- cmd.exe /C dir $someDir
>
> so I'm thinking it has something to do with the &&, hence my question.
>
> One more thing.  Such commands did work a few months ago so something
> has changed.
>
> I see this on Windows 10 using both Tcl 8.6.9 and 8.6.12.
>
> Thanks in advance for any help/insights.
>
> -mike

>Hello,
>
>If Tcl's "exec" command is used to execute a command, how does one see
>the exact command that is issued to the OS?
>
>I'm asking this question because I'm investigating the failure of
>statements such as:
>
> set someDir C:[file nativename /Users]
> exec -- cmd.exe /C cd $someDir && dir
Hello Mike,
I think you need quotes: Try
exec -- cmd.exe /C "cd $someDir" && "dir"
or
exec -- cmd.exe /C "cd $someDir" && dir
both worked on my Windows 10, 64 bit system.
Note, that when 'exec' returns I was still in my original directory,
but I could of course 'cd' from within Tcl.
I don't know what you want to do but did you have a look at 'glob'?

HTH
Helmut

>
>However, this alternative does work:
>
> exec -- cmd.exe /C "cd $someDir && dir"
>
>but I don't understand why.
>
Hello Mike,
I don't know how good your German is but here goes:
Hinweis: Mehrere Befehle, die durch das Befehlstrennzeichen "&&"
getrennt sind, werden als Zeichenfolge akzeptiert, wenn diese von
Anführungsstrichen umgeben sind.
My translation: Note: Several commands separated by "&&" are accepted
when they are quoted. (short form)
HTH
Helmut

PS: I got this info by typing 'help cmd' in a console window.

At Tue, 31 May 2022 15:07:31 -0400 Michael Soyka <mssr953@gmail.com> wrote:

>
> On 05/31/2022 1:08 PM, Michael Soyka wrote:
> > Hello,
> >
> > If Tcl's "exec" command is used to execute a command, how does one see
> > the exact command that is issued to the OS?
> >
> > I'm asking this question because I'm investigating the failure of
> > statements such as:
> >
> >     set someDir C:[file nativename /Users]
> >     exec -- cmd.exe /C cd $someDir && dir
> >
> > which responds: "The system cannot find the path specified."
>
> However, this alternative does work:
>
> exec -- cmd.exe /C "cd $someDir && dir"
>
> but I don't understand why.

I'm guessing that "cmd.exe /C <mumble>" is MS-Windows's way of doing "sh -c
<mumble>". My guess, like sh -c <mumble>, there are some gotchas relating to
how you need to quote things. You want to create a subshell and run something
like a pipeline there. You need to make sure the whole pipeline is passed to
the subshell, so you need to make the pipeline *one* argument ("cd $someDir &&
dir"), not 4 arguments (cd, $someDir, &&, dir). If you don't, you end up
passing just cd to cmd.exe /C, and then you have the three options "$someDir",
"&&", and "dir" leftover.

>
> >
> > If I disable command extensions:
> >
> >     exec -- cmd.exe /E:OFF /C cd $someDir && dir
> >
> > I don't get an error but I don't get the expected list of files either.
> >
> > However, this command works as expected:
> >
> >     exec -- cmd.exe /C dir $someDir
> >
> > so I'm thinking it has something to do with the &&, hence my question.
> >
> > One more thing.  Such commands did work a few months ago so something
> > has changed.
> >
> > I see this on Windows 10 using both Tcl 8.6.9 and 8.6.12.
> >
> > Thanks in advance for any help/insights.
> >
> > -mike
>
>
>

--
Robert Heller -- Cell: 413-658-7953 GV: 978-633-5364
Deepwoods Software -- Custom Software Services
http://www.deepsoft.com/ -- Linux Administration Services
heller@deepsoft.com -- Webhosting Services

On 05/31/2022 3:31 PM, Helmut Giese wrote:
>> Hello,
>>
>> If Tcl's "exec" command is used to execute a command, how does one see
>> the exact command that is issued to the OS?
>>
>> I'm asking this question because I'm investigating the failure of
>> statements such as:
>>
>> set someDir C:[file nativename /Users]
>> exec -- cmd.exe /C cd $someDir && dir
> Hello Mike,
> I think you need quotes: Try
> exec -- cmd.exe /C "cd $someDir" && "dir"
> or
> exec -- cmd.exe /C "cd $someDir" && dir
> both worked on my Windows 10, 64 bit system.
> Note, that when 'exec' returns I was still in my original directory,
> but I could of course 'cd' from within Tcl.
> I don't know what you want to do but did you have a look at 'glob'?

Thanks Helmut for the suggestion but my example is misleading.

My goal is to use a single shell to execute a sequence of commands. I
crafted the above example to demonstrate the problem with as simple an
example as I could.

>
> HTH
> Helmut

On 05/31/2022 3:38 PM, Helmut Giese wrote:
>>
>> However, this alternative does work:
>>
>> exec -- cmd.exe /C "cd $someDir && dir"
>>
>> but I don't understand why.
>>
> Hello Mike,
> I don't know how good your German is but here goes:
> Hinweis: Mehrere Befehle, die durch das Befehlstrennzeichen "&&"
> getrennt sind, werden als Zeichenfolge akzeptiert, wenn diese von
> Anführungsstrichen umgeben sind.
> My translation: Note: Several commands separated by "&&" are accepted
> when they are quoted. (short form)

Sorry but my German is extremely limited!
Nonetheless, I'm somewhat confused by what "help cmd" displays.

However, the following does work in a cmd window without the double quotes:

cmd.exe /C cd $someDir && dir

> HTH
> Helmut
>
> PS: I got this info by typing 'help cmd' in a console window.

On 05/31/2022 3:50 PM, Robert Heller wrote:
> At Tue, 31 May 2022 15:07:31 -0400 Michael Soyka <mssr953@gmail.com> wrote:
>
>>
>> On 05/31/2022 1:08 PM, Michael Soyka wrote:
>>> Hello,
>>>
>>> If Tcl's "exec" command is used to execute a command, how does one see
>>> the exact command that is issued to the OS?
>>>
>>> I'm asking this question because I'm investigating the failure of
>>> statements such as:
>>>
>>>     set someDir C:[file nativename /Users]
>>>     exec -- cmd.exe /C cd $someDir && dir
>>>
>>> which responds: "The system cannot find the path specified."
>>
>> However, this alternative does work:
>>
>> exec -- cmd.exe /C "cd $someDir && dir"
>>
>> but I don't understand why.
>
> I'm guessing that "cmd.exe /C <mumble>" is MS-Windows's way of doing "sh -c
> <mumble>". My guess, like sh -c <mumble>, there are some gotchas relating to
> how you need to quote things. You want to create a subshell and run something
> like a pipeline there. You need to make sure the whole pipeline is passed to
> the subshell, so you need to make the pipeline *one* argument ("cd $someDir &&
> dir"), not 4 arguments (cd, $someDir, &&, dir). If you don't, you end up
> passing just cd to cmd.exe /C, and then you have the three options "$someDir",
> "&&", and "dir" leftover.

I agree that that appears to be true. However, the "exec" man page says
(to me) that each "exec" argument represents a subprocess. Under that
assumption I don't understand why "cmd.exe", "/C" and the rest should be
formatted as 3 Tcl words (neither 1 nor 2 work).

I'm reviewing what I think is the relevant Tcl source code
(tclWinPipe.c) but, so far, it's been tough sledding!

>
>>
>>>
>>> If I disable command extensions:
>>>
>>>     exec -- cmd.exe /E:OFF /C cd $someDir && dir
>>>
>>> I don't get an error but I don't get the expected list of files either.
>>>
>>> However, this command works as expected:
>>>
>>>     exec -- cmd.exe /C dir $someDir
>>>
>>> so I'm thinking it has something to do with the &&, hence my question.
>>>
>>> One more thing.  Such commands did work a few months ago so something
>>> has changed.
>>>
>>> I see this on Windows 10 using both Tcl 8.6.9 and 8.6.12.
>>>
>>> Thanks in advance for any help/insights.
>>>
>>> -mike
>>
>>
>>
>

At Tue, 31 May 2022 16:29:09 -0400 Michael Soyka <mssr953@gmail.com> wrote:

>
> On 05/31/2022 3:50 PM, Robert Heller wrote:
> > At Tue, 31 May 2022 15:07:31 -0400 Michael Soyka <mssr953@gmail.com> wrote:
> >
> >>
> >> On 05/31/2022 1:08 PM, Michael Soyka wrote:
> >>> Hello,
> >>>
> >>> If Tcl's "exec" command is used to execute a command, how does one see
> >>> the exact command that is issued to the OS?
> >>>
> >>> I'm asking this question because I'm investigating the failure of
> >>> statements such as:
> >>>
> >>>     set someDir C:[file nativename /Users]
> >>>     exec -- cmd.exe /C cd $someDir && dir
> >>>
> >>> which responds: "The system cannot find the path specified."
> >>
> >> However, this alternative does work:
> >>
> >> exec -- cmd.exe /C "cd $someDir && dir"
> >>
> >> but I don't understand why.
> >
> > I'm guessing that "cmd.exe /C <mumble>" is MS-Windows's way of doing "sh -c
> > <mumble>". My guess, like sh -c <mumble>, there are some gotchas relating to
> > how you need to quote things. You want to create a subshell and run something
> > like a pipeline there. You need to make sure the whole pipeline is passed to
> > the subshell, so you need to make the pipeline *one* argument ("cd $someDir &&
> > dir"), not 4 arguments (cd, $someDir, &&, dir). If you don't, you end up
> > passing just cd to cmd.exe /C, and then you have the three options "$someDir",
> > "&&", and "dir" leftover.
>
> I agree that that appears to be true. However, the "exec" man page says
> (to me) that each "exec" argument represents a subprocess. Under that
> assumption I don't understand why "cmd.exe", "/C" and the rest should be
> formatted as 3 Tcl words (neither 1 nor 2 work).

The various "words" after /C are one logic operand to cmd.exe, just like the
"words" after the -c are in the case of Unix's sh. In both cases, all of the
"words" need to be collected as a single "word". This is done with quotes.

You are also misreading the exec man page. The exec command creates 1
subprocess for its first word and passes the remaining words as arguments,
possibly with special considerations for things that look like command
separaters (&&, |, ;). I guessing that since you are being upfront with
cmd.exe, you actually want something different, esp. since the cd command is a
built-in and never forks (and it makes no sense to fork it). What you want
here is a "subshell" (hense the use of "cmd.exe /C"), to handle all of your
commands. So, you need to bundle them up (with quote marks).

Basically, using "cmd.exe /C" (or "sh -c") is a special case requiring special
handling. It may or may not make sense to create a .bat (or .sh) file instead,
depending on the complexity. Then you would just run the .bat (or .sh) file:

set fp [open "temp.bat" w]
puts $fp "cd $someDir"
puts $fp "dir"
close $fp
exec cmd.exe temp.bat
file delete -force temp.bat

>
> I'm reviewing what I think is the relevant Tcl source code
> (tclWinPipe.c) but, so far, it's been tough sledding!
>
> >
> >>
> >>>
> >>> If I disable command extensions:
> >>>
> >>>     exec -- cmd.exe /E:OFF /C cd $someDir && dir
> >>>
> >>> I don't get an error but I don't get the expected list of files either.
> >>>
> >>> However, this command works as expected:
> >>>
> >>>     exec -- cmd.exe /C dir $someDir
> >>>
> >>> so I'm thinking it has something to do with the &&, hence my question.
> >>>
> >>> One more thing.  Such commands did work a few months ago so something
> >>> has changed.
> >>>
> >>> I see this on Windows 10 using both Tcl 8.6.9 and 8.6.12.
> >>>
> >>> Thanks in advance for any help/insights.
> >>>
> >>> -mike
> >>
> >>
> >>
> >
>
>
>

--
Robert Heller -- Cell: 413-658-7953 GV: 978-633-5364
Deepwoods Software -- Custom Software Services
http://www.deepsoft.com/ -- Linux Administration Services
heller@deepsoft.com -- Webhosting Services