echo(1): Clarify portability and mention literal "--" handling.

MFC after:	1 week

1 files changed, 22 insertions, 9 deletions

diff --git a/bin/echo/echo.1 b/bin/echo/echo.1
index 5f7123e..f1f3907 100644
--- a/bin/echo/echo.1
+++ b/bin/echo/echo.1
@@ -32,7 +32,7 @@
 .\"	@(#)echo.1	8.1 (Berkeley) 7/22/93
 .\" $FreeBSD$
 .\"
-.Dd April 12, 2003
+.Dd November 12, 2010
 .Dt ECHO 1
 .Os
 .Sh NAME
@@ -56,24 +56,37 @@ The following option is available:
 .Bl -tag -width flag
 .It Fl n
 Do not print the trailing newline character.
-This may also be achieved by appending
+.El
+.Pp
+The end-of-options marker
+.Fl Fl
+is not recognized and written literally.
+.Pp
+The newline may also be suppressed by appending
 .Ql \ec
 to the end of the string, as is done
 by iBCS2 compatible systems.
-Note that this option as well as the effect of
+Note that the
+.Fl n
+option as well as the effect of
 .Ql \ec
 are implementation-defined in
 .St -p1003.1-2001
 as amended by Cor.\& 1-2002.
-Applications aiming for maximum
-portability are strongly encouraged to use
+For portability,
+.Nm
+should only be used if the first argument does not start with a hyphen
+.Pq Ql "-"
+and does not contain any backslashes
+.Pq Ql "\e" .
+If this is not sufficient,
 .Xr printf 1
-to suppress the newline character.
-.El
+should be used.
 .Pp
-Some shells may provide a builtin
+Most shells provide a builtin
 .Nm
-command which is similar or identical to this utility.
+command which tends to differ from this utility
+in the treatment of options and backslashes.
 Consult the
 .Xr builtin 1
 manual page.