[src/trunk]: src/bin/echo echo.1: add a note about other echo implementations

[gutteridge <gutteridge%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/2c68a561030e
branches:  trunk
changeset: 745244:2c68a561030e
user:      gutteridge <gutteridge%NetBSD.org@localhost>
date:      Wed Feb 26 02:09:46 2020 +0000

description:
echo.1: add a note about other echo implementations

The other BSDs all have a note reminding that many shells have their
own internal echo implementations which may vary from this utility, so
add one. (Much of the wording is borrowed from FreeBSD's man page.)

(The other BSDs also have notes about the -n option not really being
portable, and printf[1] being preferable, we might want to add
something about that, too.)

diffstat:

 bin/echo/echo.1 |  15 +++++++++++++--
 1 files changed, 13 insertions(+), 2 deletions(-)

diffs (39 lines):

diff -r a15ca4f41fd6 -r 2c68a561030e bin/echo/echo.1
--- a/bin/echo/echo.1   Tue Feb 25 21:41:38 2020 +0000
+++ b/bin/echo/echo.1   Wed Feb 26 02:09:46 2020 +0000
@@ -1,4 +1,4 @@
-.\"    $NetBSD: echo.1,v 1.17 2017/07/04 06:48:41 wiz Exp $
+.\"    $NetBSD: echo.1,v 1.18 2020/02/26 02:09:46 gutteridge Exp $
 .\"
 .\" Copyright (c) 1990, 1993
 .\"    The Regents of the University of California.  All rights reserved.
@@ -32,7 +32,7 @@
 .\"
 .\"    @(#)echo.1      8.1 (Berkeley) 7/22/93
 .\"
-.Dd August 14, 2016
+.Dd February 26, 2020
 .Dt ECHO 1
 .Os
 .Sh NAME
@@ -54,9 +54,20 @@
 .It Fl n
 Do not print the trailing newline character.
 .El
+.Pp
+Note that many shells (e.g.,
+.Xr csh 1
+and
+.Xr ksh 1 )
+provide a built-in
+.Nm
+command which tends to differ from this utility in the treatment of options
+and backslashes.
 .Sh EXIT STATUS
 .Ex -std echo
 .Sh SEE ALSO
+.Xr csh 1
+.Xr ksh 1
 .Xr printf 1
 .Sh STANDARDS
 The