refactor/robust(c): use printf 💪 instead of echo; use if-else…

… instead of `&&-||`

NOTE:

- the `echo` option(e.g. -e -n) may effect correctness, `printf` is more robust 💪
- about `&&-||` see shell check:
  https://www.shellcheck.net/wiki/SC2015

bin/c

@@ -35,12 +35,14 @@ readonly PROG_VERSION='2.5.0-dev'
 # util functions
 ################################################################################
 
-readonly ec=$'\033'      # escape char
-readonly eend=$'\033[0m' # escape end
-readonly nl=$'\n'        # new line
-
-redEcho() {
-  [ -t 1 ] && echo "${ec}[1;31m$*$eend" || echo "$*"
+printErrorMsg() {
+  # check isatty in bash https://stackoverflow.com/questions/10022323
+  # if stdout is console, print with red color.
+  if [ -t 1 ]; then
+    printf "\033[1;31m%s\033[0m\n\n" "Error: $*"
+  else
+    printf '%s\n\n' "Error: $*"
+  fi
 }
 
 usage() {
@@ -49,7 +51,7 @@ usage() {
   # shellcheck disable=SC2015
   [ "$exit_code" != 0 ] && local -r out=/dev/stderr || local -r out=/dev/stdout
 
-  (($# > 0)) && redEcho "$*$nl" >$out
+  (($# > 0)) && printErrorMsg "$*" >$out
 
   cat >$out <<EOF
 Usage: ${PROG} [OPTION]... [command [command_args ...]]
@@ -73,7 +75,7 @@ EOF
 }
 
 progVersion() {
-  echo "$PROG $PROG_VERSION"
+  printf '%s\n' "$PROG $PROG_VERSION"
   exit
 }
 
@@ -106,7 +108,7 @@ while [ $# -gt 0 ]; do
     break
     ;;
   -*)
-    usage 2 "${PROG}: unrecognized option '$1'"
+    usage 2 "unrecognized option '$1'"
     ;;
   *)
     # if not option, treat all follow args as command