ps output line length (was: svn commit: r314685 - head/bin/ps)

[John Baldwin]

On Sunday, January 28, 2018 10:22:56 AM Mike Karels wrote:
> Recently, I was investigating an issue with top on -current while doing
> a "make buildworld", and ran "ps axu|more" for comparison.  To my surprise,
> I got only a few very long lines of output, containing full command lines
> for compiler runs.  This quickly led me to the following commit, which
> I unfortunately missed at the time, along with the following discussion:
> 
> > Author: cem
> > Date: Sat Mar  4 22:38:10 2017
> > New Revision: 314685
> > URL: https://svnweb.freebsd.org/changeset/base/314685
> 
> > Log:
> >   ps(1): Only detect terminal width if stdout is a tty
> >   
> >   If stdout isn't a tty, use unlimited width output rather than truncating to
> >   79 characters.  This is helpful for shell scripts or e.g., 'ps | grep foo'.
> >   
> >   This hardcoded width has some history: In The Beginning of History[0], the
> >   width of ps was hardcoded as 80 bytes.  In 1985, Bloom@ added detection
> >   using TIOCGWINSZ on stdin.[1]  In 1986, Kirk merged a change to check
> >   stdout's window size instead.  In 1990, the fallback checks to stderr and
> >   stdin's TIOCGWINSZ were added by Marc@, with the commit message "new
> >   version."[2]
> >   
> >   OS X Darwin has a very similar modification to ps(1), which simply sets
> >   UNLIMITED for all non-tty outputs.[3]  I've chosen to respect COLUMNS
> >   instead of behaving identically to Darwin here, but I don't feel strongly
> >   about that.  We could match OS X for parity if that is desired.
> >   
> >   [0]: https://svnweb.freebsd.org/csrg/bin/ps/ps.c?annotate=1065
> >   [1]: https://svnweb.freebsd.org/csrg/bin/ps/ps.c?r1=18105&r2=18106
> >   [2]:
> >   https://svnweb.freebsd.org/csrg/bin/ps/ps.c?r1=40675&r2=40674&pathrev=40675
> >   [3]:
> >   https://opensource.apple.com/source/adv_cmds/adv_cmds-168/ps/ps.c.auto.html
> >   
> >   PR:		217159
> >   Reported by:	Deepak Nagaraj <n.deepak at gmail.com>
> 
> > Modified:
> >   head/bin/ps/ps.c
> 
> > Modified: head/bin/ps/ps.c
> > ==============================================================================
> > --- head/bin/ps/ps.c	Sat Mar  4 22:23:59 2017	(r314684)
> > +++ head/bin/ps/ps.c	Sat Mar  4 22:38:10 2017	(r314685)
> > @@ -194,6 +194,8 @@ main(int argc, char *argv[])
> >  
> >  	if ((cols = getenv("COLUMNS")) != NULL && *cols != '\0')
> >  		termwidth = atoi(cols);
> > +	else if (!isatty(STDOUT_FILENO))
> > +		termwidth = UNLIMITED;
> >  	else if ((ioctl(STDOUT_FILENO, TIOCGWINSZ, (char *)&ws) == -1 &&
> >  	     ioctl(STDERR_FILENO, TIOCGWINSZ, (char *)&ws) == -1 &&
> >  	     ioctl(STDIN_FILENO,  TIOCGWINSZ, (char *)&ws) == -1) ||
> 
> There were several following messages discussing this change, most notably
> one by Bruce Evans
> (https://docs.freebsd.org/cgi/getmsg.cgi?fetch=55022+0+archive/2017/svn-src-head/20170312.svn-src-head).
> I agree with his rational, and disagree with the change.  It seems to me
> that the consensus was that the change was incorrect, although that might
> just be my opinion.  However, I really think that the change needs to be
> reverted.
> 
> The rationale for the original code was that, for interactive uses, the
> output line length should be the same for "ps ...", "ps ...|more", and
> "ps ... |grep".  The -w option exists to make the line longer; there is
> no option to use the terminal size even if the output is redirected.
> Hence, the tests for stderr or stdin being a tty.  This behavior has
> been in place since 1990, as noted, and no substantial rationale has
> been given for changing it other than "it doesn't matter if you use
> less with side-to-side scrolling."  fwiw, I'm sure I discussed that
> code with Marc at the time.
> 
> As was stated, scripts that want to use the full line should use -ww.
> Interactive users have long been used to using -w when they need longer
> output lines, e.g. to match patterns that don't occur within a screen's
> width.
> 
> I propose reverting this change.

I do feel like I've always assumed I needed -ww if I wanted long lines to
be deterministic.  This feels like it breaks interactive 'ps | grep foo'
on a desktop with lots of long command lines (e.g. with KDE or the like)
as you lose the single-line output of the original interactive 'ps'.

-- 
John Baldwin