Re: bin/57253: xargs wraps lines after ~4k characters

[Robert Elz <kre%munnari.OZ.AU@localhost>]

The following reply was made to PR bin/57253; it has been noted by GNATS.

From: Robert Elz <kre%munnari.OZ.AU@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: marc%fege.net@localhost, rvp%sdf.org@localhost, netbsd-bugs%netbsd.org@localhost
Subject: Re: bin/57253: xargs wraps lines after ~4k characters
Date: Thu, 02 Mar 2023 20:24:25 +0700

     Date:        Thu,  2 Mar 2023 11:45:02 +0000 (UTC)
     From:        Marc Daniel Fege <marc%fege.net@localhost>
     Message-ID:  <20230302114502.386241A923B%mollari.NetBSD.org@localhost>
 
   |  Indeed, some limit will be there anyway. But do those limits need to be
   |  (artificially) defined in the userland programs themselves to handle an
   |  otherwise comming up exception of the programming language or library?
 
 In the case of xargs, POSIX actually requires it:
 
 	The generated command line length shall be the sum of the size
 	in bytes of the utility name and each argument treated as strings,
 	including a null byte terminator for each of these strings. The
 	xargs utility shall limit the command line length
 
 "shall" in POSIX means it is an absolute requirement - that must happen.
 
 	such that when the command line is invoked, the combined argument
 	and environment lists (see the exec family of functions in the System
 	Interfaces volume of POSIX.1-202x) shall not exceed {ARG_MAX}-2048
 	bytes. Within this constraint, if neither the -n nor the -s option
 	is specified, the default command line length shall be at least
 	{LINE_MAX}.
 
 If you chase enough definitions in XCU 1.2 (Utility Limits) you'll
 discover that the minimum value for LINE_MAX is 2048.  ARG_MAX is
 defined in the specification of <limits.h> in XSH 14.   That ends up
 being 4096 (minimum).
 
 If you want to write a portable script, you need to expect those limits
 on some systems.   I doubt our xargs limits anything to 4K, I think we
 get quite close to the implementation limit (much more than you are
 entitled to reply upon) - but do note that what is in the environment
 counts, if you have lots of stuff there, xargs will make shorter commands
 (less args) then if you have less in the environment.   Both the number
 of environment variables, and the length of each of those (NAME=value)
 matters.
 
 kre