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Re: Perl ignores lines with bold characters from a pipe on Windows (source not dest)
by tye (Sage) on Mar 03, 2007 at 03:14 UTC
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I strongly suspect that the answer that explains this will actually be to the question "Why doesn't mycmd write the lines that would contain bold characters when I launch it these ways from Perl?".
The third case is especially indicative as Perl isn't doing any of the "problem" I/O so how can Perl be ignoring any lines? Perl isn't between mycmd and test_perl3 so the contents of test_perl3 have nothing to with Perl's I/O features nor could Perl "ignore" things and have any impact on what ends up in test_perl3.
You need to discard your theory that Perl is ignoring lines and look at the problem again. There are other test cases you can try (running mycmd vs. perl -e"system('mycmd')", for example). You should look for more information about mycmd also.
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Probably correct. Unfortunately I have no idea how mycmd might be analyzing its parent process. To my knowledge no relevant environment variables are set either from the shell or from Perl. Mycmd is closed source, so I'm likely at a dead end.
How can I check that Perl isn't setting any environment variables?
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How can I check that Perl isn't setting any environment variables?
AFAIK, it doesn't. If you don't, that is. OTOH under *NIX it is possible to detect whether a file descriptor is connected to a tty or not, which is often used to "understand" whether a program's STDOUT is being piped or redirected to a file or not. (This is what e.g. ls(1) does under recent releases of Linux, at least: it acts like ls -1 if you pipe it to something else, and similarly if you set --color=auto it will print coloured output on the terminal, but will disable it when piping or redirecting to a file - in fact the switch is set by default in many distros.) Maybe under windows it's the same. Let me see:
C:\temp>perl -le "open F, '>F'; print -t *F; print -t *STDOUT"
1
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Re: Perl ignores lines with bold characters from a pipe on Windows
by almut (Canon) on Mar 03, 2007 at 04:25 UTC
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Just a wild guess: your mycmd might be mixing output via
redirectable streams with "direct" console output via WriteConsole.
AFAIK, the latter would typically be used to render highlighted text
etc., making use of console "attributes". In particular, note that
Both WriteConsole and WriteFile can be used for console I/O. While
WriteConsole supports writing Unicode characters to a console screen
buffer, WriteFile does not. However, WriteConsole fails if it is used
with a standard handle that is redirected to a file. (... more)
(emphasis added)
This might explain why some lines get lost when capturing redirectable output only (stdout).
As to why the console output does end up in the file test_shell when redirecting output from the shell command line, I don't know. Maybe some additional magic is going on in this case...(?)
Anyway, what kind of program is this? Do you have the sources? If
not, you might try a tool like StraceNT
to find out what API calls are being used... (in particular look for
WriteConsole, WriteFile, etc.)
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This is a port from Unix (cleartool), so I doubt it's MS api oddities.
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I think it is the Win32 API oddity, as the Win32 console has no ANSI or terminal emulation. If you want to output any color or weirdo formatting, you have to output these by directly writing to the console window yourself, bypassing the STDOUT filehandle. Hence I guess that the programmers wanted to keep their fancy feature of bold output and hence destroyed the ability to redirect the whole output.
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Re: Perl ignores lines with bold characters from a pipe on Windows
by pKai (Priest) on Mar 03, 2007 at 09:34 UTC
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As proposed by tye you should be able to test the different theories mentioned in other replies.
Check different scenarios on a plain cmd command line.
| command | output seen in/on | interpretation |
|---|
| out | err | screen |
| 1. | mycmd >out 2>err | + | - | + | almut |
| 2. | + | + | - | Joost |
| … | other? | post it, and someone will explain |
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Re: Perl ignores lines with bold characters from a pipe on Windows
by Joost (Canon) on Mar 03, 2007 at 02:27 UTC
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If you were on UNIX I'd guess the bold lines were printed to STDERR instead of STDOUT and so wouldn't be redirected by the mycmd > test_perl3 line. Possibly the same thing would happen on windows.
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Definitely nothing going to STDERR.
In case it matters, the bold lines look this:
C:\a\file [AFLAG]
Perhaps the bolded '[' means something to perl IO? I'm grasping at straws.
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In case it matters, the bold lines look this:
C:\a\file [AFLAG]
Well, text is text, and it knows no intrinsic notion of charachter attributes, like bold. However one early, conceptually simple and long-lasting strategy to achieve them was and is by means of ANSI escape codes: support for them is built in under Linux. Back in the days of good 'ol DOS, you would use the ANSI.SYS device driver to enable them. (And at some point ANSI art flourished.) This remained possible up to the 9.x Windows releases, but NT based ones do not support it anymore, which is the reason why dedicated ANSI art viewers and, speaking of Perl, a module like Win32::Console::ANSI exist. Thus a program that wants to output charachters with attributes under recent Windowsen needs to dialogue directly with the console APIs, e.g. in Perl by means of Win32::Console upon which Win32::Console::ANSI relies. Chances are that it is not perl that "ignores" lines with bold charachters, but that those lines are not printed to STDOUT at all.
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