doc: improve factor example

* doc/coreutils.texi (factor invocation): Adjust example to use $(...)
consistently, not a mix of `...` and $(...).  Separate the computation
of the product and the actual factorization, so the timing of the
latter doesn't include the cost of the former.

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index c26a53d..c229f98 100644 (file)
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -15964,8 +15964,10 @@ Factoring the product of the eighth and ninth Mersenne primes
 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
 
 @example
-M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
-/usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
+M8=$(echo 2^31-1|bc)
+M9=$(echo 2^61-1|bc)
+n=$(echo "$M8 * $M9" | bc)
+/usr/bin/time -f %U factor $n
 4951760154835678088235319297: 2147483647 2305843009213693951
 0.03
 @end example