Newt!

Newt is a trivially simple template instantianion tool. WTF is a template instatiotion tool? It turns files with named fields into files without named fields!

Say you just spent twelve hours Yak-shaving to get a configuration file tweaked just right, and your friends want to use it. However, the configuration file has your user name and password in it, so you can't just share the file with them. At the very least, you have to replace those values, then tell your friends where to put their values, and hopefully those only occurr once in the file you need to share.

Newt can make this easier.

Here's what you do:

• make a copy of your config file somewhere so you don't break the one you actually use.
• replace your user name with the string <<<username>>>
• replace your password with the string <<<password>>>

Now, send your friends the new file with these instructions:

1. Go install newt!
2. Save this template to /tmp/myTemplate
3. run newt --source=/tmp/myTemplate --dest=<destination> username=yourUsername password=yourPassword

• Alternatively, you can leave off the --source= and --dest= bits:
  • newt /tmp/myTemplate <destination> username=yourUsername password=yourPassword

4. There you go. <destination> now has a populated version of the config file.

I did say Newt was trivially simple.

Aside from usernames and passwords, you can use newt to replace any string key with any string value, as long as none of the keys include ">>>" or "=". It might even handle unicode someday.

I hope this is handy for writing scripts that need to set configuration files, or if you write a lot of LaTeX documents, and you want to fill in boiler plate from a command line. I also have grand design for pointing newt at a tarball of templates and having it expand the tarball while fleshing out the details. For now, you get to work with one file at a time.

Examples

Create a new cabal project!

Input File (in.cabal):

name:                <<<name>>>
version:             0.0.0.1
synopsis:            <<<synopsis>>>
description:         <<<description>>>
category:            Tools
license:             BSD3
License-file:        LICENSE
author:              <<<author>>>
maintainer:          <<<authoremail>>>
Cabal-Version:       >=1.8.0.6
build-type:          Simple

Executable <<<name>>>
   Main-Is:          Main.hs
   hs-source-dirs:   src

Newt command:

$ newt --source=in.cabal --dest=FooApp.cabal name=FooApp author="Rogan Creswick" authoremail=creswick@someemail.com

Result (in FooApp.cabal):

name:                FooApp
version:             0.0.0.1
synopsis:            <<<synopsis>>>
description:         <<<description>>>
category:            Tools
license:             BSD3
License-file:        LICENSE
author:              Rogan Creswick
maintainer:          creswick@someemail.com
Cabal-Version:       >=1.8.0.6
build-type:          Simple

Executable FooApp
   Main-Is:          Main.hs
   hs-source-dirs:   src

Note that the author needed to be put in quotes to prevent the shell from splitting the author="Rogan Creswick" argument to Newt into two arguments.

Also note that we didn't need to define synopsis or description. They remain in the file, so you can partially fill a template if you want.

List the keys

Newt can also tell you which keys you can specify for a given template. If you don't know what the valid keys are, then just run newt with --list:

$ newt --source=in.cabal --list
author
authoremail
description
name
synopsis