Updated SC2039 (markdown)

SC2039.md

@@ -101,7 +101,8 @@ grep aaa <<< "$g"
 POSIX:
 
 ```sh
-printf '%s' "$g" | grep aaa # since we want to avoid `echo`
+# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
+printf '%s' "$g" | grep aaa
 ```
 
 ### echo flags
@@ -138,7 +139,10 @@ POSIX:
 # TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
 # See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
 reuse_quote()(
-  for i; do echo -n \'; echo -n "$i" | sed -e "s/'/'\\\\''/g"; echo -n "' "; done
+  for i; do
+    __i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
+    printf "'%s'" "${__i_quote%x}"
+  done
 )
 reuse_quote "$@"
 ```