watch: add additional notes about environment

References:
 procps-ng/procps!62
 commit d3e0ff5a0a

NEWS

@@ -10,6 +10,7 @@ procps-ng NEXT
   * top: ensure config file backward compatibility         Debian #951335
   * top: add command line 'e' for symmetry with 'E'        issue #165
   * vmstat: Wide mode gives wider proc columns             merge #48
+  * watch: Add environment variable for interval           merge #62
 
 procps-ng-3.3.16
 ----------------

watch.1

@@ -1,4 +1,4 @@
-.TH WATCH 1 "2018-03-03" "procps-ng" "User Commands"
+.TH WATCH 1 "2020-05-12" "procps-ng" "User Commands"
 .SH NAME
 watch \- execute a program periodically, showing output fullscreen
 .SH SYNOPSIS
@@ -101,6 +101,16 @@ failed, or command exited up on error.
 .TP
 .B other
 The watch will propagate command exit status as child exit status.
+.SH ENVIRONMENT
+The behaviour of
+.B watch
+is affected by the following environment variables.
+
+.TP
+.B WATCH_INTERVAL
+Update interval, follows the same rules as the
+.B \-\-interval
+command line option.
 .SH NOTES
 POSIX option processing is used (i.e., option processing stops at
 the first non\-option argument).  This means that flags after

watch.c

@@ -706,7 +706,7 @@ int main(int argc, char *argv[])
 	atexit(close_stdout);
 
 	interval_string = getenv("WATCH_INTERVAL");
-	if(interval_string != NULL) 
+	if(interval_string != NULL)
 		interval = strtod_nol_or_err(interval_string, _("Could not parse interval from WATCH_INTERVAL"));
 
 	while ((optc =