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yet another boundary in cmd (pipes)
Posted: 10 May 2015 05:20
by npocmaka_
max sequence of pipes is 2042 .The 2043th produces "The handle could not be duplicated during a pipe operation." (tested on Win8x64 and WinXPx32.Not tested with conditional operators or cyclic stream redirections .):
https://gist.github.com/npocmaka/ee9ed4bf3a83b0910ff5
Re: yet another boundary in cmd (pipes)
Posted: 10 May 2015 13:23
by penpen
Re: yet another boundary in cmd (pipes)
Posted: 10 May 2015 13:44
by npocmaka_
Aahh.Most probably as each pipe starts subprocess of cmd.Thanks for the link.
Re: yet another boundary in cmd (pipes)
Posted: 11 May 2015 02:36
by jeb
Even if the point of penpen is the real cause, the finding is quite interessant, but for a complete other reason
You bring me to another idea to be tested.
Code: Select all
@echo off
setlocal
set "var=12345678901234567890"
(
echo @echo off
<nul set /p ".=echo %var%"
for /L %%n in (1 1 2000) DO (
<nul set /p ".= | find "%var%" "
)
echo(
) > longLine.bat
call longLine.bat
for %%a in ("longLine.bat") DO echo It works, %%a is %%~za bytes long
This creates a batch with the second line looks like
Code: Select all
echo 12345678901234567890 | find "12345678901234567890" | find "12345678901234567890" | find .... | find "12345678901234567890" "
The line is about
60.000 characters long and it still works
So the line limit of 8191 bytes is not always fix as thought it was.
Perhaps it can be useful for things like macros or something else
Re: yet another boundary in cmd (pipes)
Posted: 11 May 2015 23:46
by foxidrive
jeb wrote:So the line limit of 8191 bytes is not always fix as thought it was.
I wonder if it is 8191 per pipe?
Re: yet another boundary in cmd (pipes)
Posted: 12 May 2015 05:06
by dbenham
Very cool jeb.
Can you fix your output? It does not match your posted script.
I don't remember the details, but I do remember you demonstrated that FOR /F has a limited ability to read lines longer than 8191 bytes long. Can you think of a way to usefully combine the FOR /F capability with this new discovery?
Dave Benham