Add helper script to set docker env (#35)

* Add helper script to set docker environment

* Add README

README.md

@@ -26,9 +26,20 @@ $ curl -sL https://raw.githubusercontent.com/at-wat/gh-pr-comment/master/install
 
 ## Required environment variables
 
-### Travis-CI
+To run gh-pr-comment inside docker container, required environemnt variables can be automatically specified by the following script.
+```shell
+$ docker run [your options...] \
+    $(bash <(curl -s https://raw.githubusercontent.com/at-wat/gh-pr-comment/master/env.sh)) \
+    image commands...
+```
 
+### General
+- ***GITHUB\_TOKEN*** (or ***TRAVIS\_BOT\_GITHUB\_TOKEN***): token with comment write permission
+
+### Optional
+- ***GITHUB\_API\_URL\_BASE***: specify GitHub Enterprise or any custom endpoint URL
+
+### Travis-CI
 - ***TRAVIS***: true
 - ***TRAVIS\_PULL\_REQUEST\_SLUG***: owner/repos
 - ***TRAVIS\_PULL\_REQUEST***: pull request number
-- ***TRAVIS\_BOT\_GITHUB\_TOKEN*** or ***GITHUB\_TOKEN***: token with comment write permission

env.sh

@@ -0,0 +1,25 @@
+#!/bin/sh
+
+# Output list of docker run options to pass required environment variables.
+
+if [ "${TRAVIS}" = "true" ]
+then
+  echo "-e TRAVIS"
+  echo "-e TRAVIS_PULL_REQUEST"
+  echo "-e TRAVIS_PULL_REQUEST_SLUG"
+fi
+
+if [ -n "${GITHUB_API_URL_BASE}" ]
+then
+  echo "-e GITHUB_API_URL_BASE"
+fi
+
+if [ -n "${GITHUB_TOKEN}" ]
+then
+  echo "-e GITHUB_TOKEN"
+fi
+
+if [ -n "${TRAVIS_BOT_GITHUB_TOKEN}" ]
+then
+  echo "-e TRAVIS_BOT_GITHUB_TOKEN"
+fi