Implement opoo in bash

Library/Homebrew/brew.sh

@@ -1,20 +1,35 @@
 HOMEBREW_VERSION="0.9.9"
 
-onoe() {
-  if [[ -t 2 ]] # check whether stderr is a tty.
-  then
-    echo -ne "\033[4;31mError\033[0m: " >&2 # highlight Error with underline and red color
-  else
-    echo -n "Error: " >&2
-  fi
+o() {
   if [[ $# -eq 0 ]]
   then
-    /bin/cat >&2
+    /bin/cat
   else
-    echo "$*" >&2
+    echo "$*"
   fi
 }
 
+highlight() {
+  if [[ -t 1 ]] # check whether stdout is a tty.
+  then
+    echo -ne "\033[4;$1m$2\033[0m"
+  else
+    echo -n "$2"
+  fi
+}
+
+opoo() {
+  highlight 33 Warning >&2 # yellow
+  echo -n ": " >&2
+  o "$@" >&2
+}
+
+onoe() {
+  highlight 31 Error >&2 # red
+  echo -n ": " >&2
+  o "$@" >&2
+}
+
 odie() {
   onoe "$@"
   exit 1