Clean way to launch the web browser from shell script?

In a bash script, I need to launch the user web browser. There seems to be many ways of doing this:

• $BROWSER
• xdg-open
• gnome-open on GNOME
• www-browser
• x-www-browser
• ...

Is there a more-standard-than-the-others way to do this that would work on most platforms, or should I just go with something like this:

#/usr/bin/env bash

if [ -n $BROWSER ]; then
  $BROWSER 'http://wwww.google.com'
elif which xdg-open > /dev/null; then
  xdg-open 'http://wwww.google.com'
elif which gnome-open > /dev/null; then
  gnome-open 'http://wwww.google.com'
# elif bla bla bla...
else
  echo "Could not detect the web browser to use."
fi

xdg-open is standardized and should be available in most distributions.

Otherwise:

1. eval is evil, don't use it.
2. Quote your variables.
3. Use the correct test operators in the correct way.

Here is an example:

#!/bin/bash
if which xdg-open > /dev/null
then
  xdg-open URL
elif which gnome-open > /dev/null
then
  gnome-open URL
fi

Maybe this version is slightly better (still untested):

#!/bin/bash
URL=$1
[[ -x $BROWSER ]] && exec "$BROWSER" "$URL"
path=$(which xdg-open || which gnome-open) && exec "$path" "$URL"
echo "Can't find browser"