GNU bug report logs - #8961
stdbuf has no effect on some programs

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Message #16 received at 8961 <at> debbugs.gnu.org (full text, mbox):

From: Bruno Haible <bruno <at> clisp.org>
To: Pádraig Brady <P <at> draigbrady.com>
Cc: 8961 <at> debbugs.gnu.org
Subject: Re: bug#8961: stdbuf has no effect on some programs
Date: Thu, 30 Jun 2011 01:34:12 +0200

Hi Pádraig,

> The following shows I think that iconv is bypassing stdio and buffering internally?
> 
> (echo; sleep 3; echo) | ltrace iconv -f ASCII

Indeed, the glibc 'iconv' does not use stdio apparently:

__libc_start_main(0x402a00, 3, 0x7fff76b92d68, 0x409c90, 0x409c80 <unfinished ...>
setlocale(6, "")                                                                                 = "de_DE.UTF-8"
textdomain("libc")                                                                               = "libc"
argp_parse(0x60d2e0, 3, 0x7fff76b92d68, 0, 0x7fff76b92c5c)                                       = 0
strchr("ASCII", '/')                                                                             = NULL
strchr("", '/')                                                                                  = NULL
iconv_open(0x409daf, 0x7fff76b946e6, 0, 0x53494c4300494900, 0xfefefefefefefeff)                  = 0x613080
fileno(0x7f4c6e9726a0)                                                                           = 0
realloc(NULL, 32768)                                                                             = 0x00615100
read(0, "\n", 32768)                                                                             = 1
read(0, "\n", 32767)                                                                             = 1
read(0, "", 32766)                                                                               = 0
iconv(0x613080, 0x7fff76b8ab38, 0x7fff76b8ab30, 0x7fff76b92b48, 0x7fff76b92b40)                  = 0
...

> The stdbuf man page notes that:
> 
> NOTE: If COMMAND adjusts the buffering of its standard  streams  (`tee'
> does  for  e.g.) then that will override corresponding settings changed
> by `stdbuf'.  Also some filters (like `dd' and `cat'  etc.)  don't  use
> streams for I/O, and are thus unaffected by `stdbuf' settings.

This paragraph is written in a way that does not make the implications
very clear. How about the attached patch, meant to show the restrictions more
prominently?


2011-06-29  Bruno Haible  <bruno <at> clisp.org>

	* doc/coreutils.texi (stdbuf invocation): Mention the restrictions on
	the command more prominently.

--- doc/coreutils.texi.orig	Thu Jun 30 01:31:13 2011
+++ doc/coreutils.texi	Thu Jun 30 01:30:54 2011
@@ -15398,6 +15398,17 @@
 stdbuf @var{option}@dots{} @var{command}
 @end example
 
+@var{command} must start with the name of a program that
+@enumerate
+@item
+uses the ISO C @code{FILE} streams for input/output (note the
+programs @command{dd} and @command{cat} don't do that),
+
+@item
+does not adjust the buffering of its standard streams (note the
+program @command{tee} is not in this category).
+@end enumerate
+
 Any additional @var{arg}s are passed as additional arguments to the
 @var{command}.
 
@@ -15446,12 +15457,6 @@
 
 @end table
 
-NOTE: If @var{command} adjusts the buffering of its standard streams
-(@command{tee} does for e.g.) then that will override corresponding settings
-changed by @command{stdbuf}.  Also some filters (like @command{dd} and
-@command{cat} etc.) don't use streams for I/O, and are thus unaffected
-by @command{stdbuf} settings.
-
 @cindex exit status of @command{stdbuf}
 Exit status:
 
-- 
In memoriam José Olaya <http://es.wikipedia.org/wiki/José_Olaya>

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