[PATCH] xargs: clarify command as optional in --help output

* xargs/xargs.c (usage): Fix synopsis by wrapping COMMAND in '[...]',
because it is in fact optional.  Also add a sentence that the default
COMMAND is 'echo'.
---
 xargs/xargs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xargs/xargs.c b/xargs/xargs.c
index 8abdd790..517f963c 100644
--- a/xargs/xargs.c
+++ b/xargs/xargs.c
@@ -1729,7 +1729,7 @@ usage (int status)
     }

   fprintf (stdout,
-           _("Usage: %s [OPTION]... COMMAND [INITIAL-ARGS]...\n"),
+           _("Usage: %s [OPTION]... [COMMAND [INITIAL-ARGS]...]\n"),
            program_name);

 #define HTL(t) fputs (t, stdout);
@@ -1775,6 +1775,7 @@ usage (int status)

   HTL (_("      --help                   display this help and exit\n"));
   HTL (_("      --version                output version information and exit\n\n"));
+  HTL (_("If COMMAND is omitted, the default is 'echo'.\n\n"));
   explain_how_to_report_bugs (stdout, program_name);
   exit (status);
 }
--
2.47.1