bin/164535: ps(1) truncates command to screen size even when stdout is not a tty

Bruce Evans brde at
Fri Jan 27 11:50:08 UTC 2012

The following reply was made to PR bin/164535; it has been noted by GNATS.

From: Bruce Evans <brde at>
To: Marcus Reid <marcus at>
Cc: freebsd-gnats-submit at, freebsd-bugs at
Subject: Re: bin/164535: ps(1) truncates command to screen size even when
 stdout is not a tty
Date: Fri, 27 Jan 2012 22:49:35 +1100 (EST)

 On Fri, 27 Jan 2012, Marcus Reid wrote:
 >> Description:
 > ps(1) truncates long commands to the size of the screen even when stdout is not a terminal.  This is counter-intuitive and differs from another implementation I looked at.  Output of ps | grep differs depending on how big your terminal window is for example.
 >> How-To-Repeat:
 > ps aux | grep
 > ps auxww | grep
 >> Fix:
 > Patch included.  Tested; behavior remains consistent with docs: COLUMNS variable retains effect, and -w limits to 132 characters still.
 > Patch attached with submission follows:
 > --- bin/ps/ps.c.orig	2012-01-27 01:24:10.519024952 -0800
 > +++ bin/ps/ps.c	2012-01-27 01:24:20.350023629 -0800
 > @@ -187,6 +187,8 @@
 > 	if ((cols = getenv("COLUMNS")) != NULL && *cols != '\0')
 > 		termwidth = atoi(cols);
 > +	else if (isatty(STDOUT_FILENO) == 0)
 > +		termwidth = UNLIMITED;
 This change defeats the else clause, which checks all of STDOUT_FILENO,
 STDERR_FILENO and STDIN_FILENO and uses the terminal width iff any if
 these is a terminal according to the TIOCGWINSZ test for being a
 terminal, and otherwise gives a default of 79 columns (not UNLIMITED,
 which is only documented for ps -ww and only reachable using that and
 via the missing sanity checking for COLUMNS=0).
 > 	else if ((ioctl(STDOUT_FILENO, TIOCGWINSZ, (char *)&ws) == -1 &&
 > 	     ioctl(STDERR_FILENO, TIOCGWINSZ, (char *)&ws) == -1 &&
 > 	     ioctl(STDIN_FILENO,  TIOCGWINSZ, (char *)&ws) == -1) ||
 So the correct way to avoid terminalness when outputting to a file
 is "ps </dev/null >foo 2>&1".  This is too strange for stdin, so
 apparently checking all 3 fd's is a feature, precisely to get the
 terminal width from somewhere even when stdout and stderr are
 redirected to a file.  "COLUMNS=0 ps" is an easier way.  If this
 feature is considered a bug, then remove the checks of STDERR_FILENO

More information about the freebsd-bugs mailing list