From d7e7d2127234f6a40c4576e7dd43c42b7386fd0c Mon Sep 17 00:00:00 2001
From: Stefan Zwanenburg <stefan@zwanenburg.info>
Date: Sat, 25 Jan 2020 05:01:09 +0100
Subject: [PATCH] Updated README

---
 README.md | 115 +++++++++++++++++++++++++++++++++---------------------
 1 file changed, 71 insertions(+), 44 deletions(-)

diff --git a/README.md b/README.md
index ff2d972..f8a8b0c 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,7 @@ container to be PID 1.
 - Mustache templates
 - Environment variables as source of data for your templates
 - Glob support for specifying templates
+- Chosing the rendered filename by search and replace of the template filename
 - Executes the binary of your choice after rendering templates
 - Errors out when rendering a template containing a reference to a non-existing
   environment variable (can be disabled with the `--allow-missing` flag)
@@ -20,63 +21,89 @@ container to be PID 1.
 ## `mustache-then-exec --help`
 
 ```
-  Replaces TEMPLATE files (which are Go globs) with their contents
-  rendered as a Mustache template, where the environment variables are
-  passed as data to those tempales.
-
-  -allow-missing
-    	Whether to allow missing variables (default: false).
+Usage: mustache-then-exec [--allow-missing] [--template TEMPLATE] [--glob-template GLOB] BINARY [ARG [ARG ...]]
+
+Positional arguments:
+  BINARY                 the binary to run after rendering the templates
+  ARG                    arguments to the binary to run after rendering the templates
+
+Options:
+  --allow-missing, -a    whether to allow missing variables (default: false)
+  --template TEMPLATE, -t TEMPLATE
+                         path to a template to be rendered
+  --glob-template GLOB, -g GLOB
+                         glob for templates to be rendered
+  --help, -h             display this help and exit
 ```
 
 ## Example
 
-Here's a Dockerfile for a simple nginx proxy:
+Here's a Dockerfile for a simple image that executes a `cat` binary:
 
 ```dockerfile
-FROM nginx:alpine
+FROM busybox
 
 COPY mustache-then-exec /
 
-RUN echo $'\
-  events { \n\
-  } \n\
-  http { \n\
-    server { \n\
-      listen 80; \n\
-      location / { \n\
-        proxy_pass {{{NGINX_PROXY_UPSTREAM}}}; \n\
-      } \n\
-    } \n\
-  }' > /etc/nginx/nginx.conf 
-
-ENTRYPOINT [ "/mustache-then-exec", "/etc/nginx/*.conf", "--", "/usr/sbin/nginx" ]
-
-CMD [ "-g", "daemon off;" ]
+RUN echo "Hello, {{{THING_TO_GREET}}}!" > /mytemplate
+
+ENTRYPOINT [ "/mustache-then-exec", "-t", "/mytemplate", "--", "/bin/cat" ]
 ```
 
 Which you can now run as follows (image name depending on how you tagged your
 image during `docker build`):
 
 ```shellsession
-$ docker run --rm -p 80:80 mustache-then-exec-nginx-proxy
-Filling template: /etc/nginx/fastcgi.conf
-Filling template: /etc/nginx/nginx.conf
-Error: Missing variable "NGINX_PROXY_UPSTREAM"
-$ docker run --rm -d -p 80:80 -e NGINX_PROXY_UPSTREAM=https://httpbin.org/get mustache-then-exec-nginx-proxy
-f3a67fa793821c3815997cfcc78a6619a01836f3c61380606922c6bf779ab30d
-$ docker exec f3a67fa793821c3815997cfcc78a6619a01836f3c61380606922c6bf779ab30d pstree -p
-nginx(1)---nginx(11)
-$ curl http://localhost:80/get
-curl http://localhost:80
-{
-  "args": {}, 
-  "headers": {
-    "Accept": "*/*", 
-    "Host": "httpbin.org", 
-    "User-Agent": "curl/7.68.0",
-  }, 
-  "origin": "1.1.1.1", 
-  "url": "https://httpbin.org/get"
-}
-$ docker kill f3a67fa793821c3815997cfcc78a6619a01836f3c61380606922c6bf779ab30d
+$ #What happens when I don't set the required environment variable?
+$ docker run --rm cat /mytemplate /mytemplate
+Rendering template: /mytemplate; output: /mytemplate
+Error: Missing variable "THING_TO_GREET"
+$ #And what happens when I set it?
+$ docker run --rm -e THING_TO_GREET=World cat /mytemplate
+Rendering template: /mytemplate; output: /mytemplate
+Hello, World!
+$ #I'm goingo tm make cat read from stdin, so that it keeps running
+$ docker run --rm -td -e THING_TO_GREET=World cat -
+c6e4910c274d7b0984924c744d147935dbd62a89fe02da3a731a9264f794020c
+$ #And now I can see what processes are running in my container: no mustache-then-exec!
+$ docker exec c6e4910c274d7b0984924c744d147935dbd62a89fe02da3a731a9264f794020c pstree -p
+cat(1)
+$ docker kill c6e4910c274d7b0984924c744d147935dbd62a89fe02da3a731a9264f794020c 
+c6e4910c274d7b0984924c744d147935dbd62a89fe02da3a731a9264f794020c
+```
+
+## Example with renaming and globbing
+
+Let's expand a little on the previous example, and add two extra features:
+
+1. Globbing
+1. Renaming with regexp search&replace
+
+Another Dockerfile that does mostly the same:
+
+```dockerfile
+FROM busybox
+
+COPY mustache-then-exec /
+
+RUN echo "Hello, {{{THING_TO_GREET}}}!" | tee /mytemplate01 /mytemplate02
+
+ENTRYPOINT [ "/mustache-then-exec", "-g", "/mytemplate*:mytemplate([0-9]+):replacement-filename-$1", "--", "/bin/cat" ]
+```
+
+And, assuming we also named this image `cat`, let's use it as follows:
+
+```shellsession
+$ #What happened to the templates?
+$ docker run --rm -e THING_TO_GREET=World cat /mytemplate01 /mytemplate02
+Rendering template: /mytemplate01; output: /replacement-filename-01
+Rendering template: /mytemplate02; output: /replacement-filename-02
+Hello, {{{THING_TO_GREET}}}!
+Hello, {{{THING_TO_GREET}}}!
+$ #And did we indeed get renamed files?
+$ docker run --rm -e THING_TO_GREET=World cat /replacement-filename-01 /replacement-filename-02
+Rendering template: /mytemplate01; output: /replacement-filename-01
+Rendering template: /mytemplate02; output: /replacement-filename-02
+Hello, World!
+Hello, World!
 ```