This is a Lua program and module that allows quick and easy templating.
This was written against luajit and tested against luajit and lua-5.1.
Please see LICENSE.txt. This is AGPL.
Define your template in a lua script. This script must return one or two values. In the case of one value, it is just the template text itself. In the case of two values, it should be the template text and a table of variables for substitution.
Run the smalltemplate script on the template file. You probably want to redirect stdout to a file, like so:
./smalltemplate my_template.txt.lua > my_template.txt
On stderr, some diagnostics will be printed.
Variables match the pattern:
${(.-)}
This matches all values like ${myvariable}, ${my_variable},
${my.variables}, ${my variable with spaces}, etc., but it does not match
greedily.
The variable lookup is done with string.gsub and a function to get the name
of the variable from the table.
It is possible to execute arbitrary lua code that only exposes the math, string, table modules present in a standard luajit or lua-5.1 install. To do this, pass the parameter "true" to the smalltemplate script call, like so:
./smalltemplate my_template.txt.lua true > my_template.txt
Please note that this is not fully sandboxed, as an attacker could change those modules and affect the outside content. I do not recommend exposing such functionality against a publicly-facing endpoint at this time.
To print a literal $ in the template, simply use this construct:
${}
The escape is only needed if the character after $ is a {. However, the
template function will naively replace all instances of ${} with $.
Hacky, but it works, and doesn't complicate the very naive gsub matcher.
If at any point that an undefined variable is referenced, the script will error. Here is an example of such an error:
$ ./smalltemplate my_error_template.txt.lua
(stderr) Templating my_error_template.txt.lua. Allowing lua evaluation in template: false
lua: ./smalltemplate.lua:32: no substitution available for variable name 'my_value': (lua evaluation not enabled)
stack traceback:
[C]: in function 'error'
./smalltemplate.lua:32: in function <./smalltemplate.lua:16>
[C]: in function 'gsub'
./smalltemplate.lua:38: in function 'template'
./smalltemplate:20: in main chunk
[C]: ?
If we fix this issue, here is what results:
$ ./smalltemplate my_error_template_fixed.txt.lua
(stderr) Templating my_error_template_fixed.txt.lua. Allowing lua evaluation in template: false
Here is my value, but it will no longer error, because I am using a lowercase V:
'my value is here, but notice the lack of capital V for the variable name'
(stderr) Templated my_error_template_fixed.txt.lua with 1 substitutions.
In MSYS-MinGW64, /usr/bin/luajit is a script with the following:
$ cat /mingw64/bin/luajit
#!/usr/bin/env bash
/usr/bin/winpty "$( dirname ${BASH_SOURCE[0]} )/luajit.exe" "$@"
This means luajit will run using winpty, which if stdout or stderr is redirected, it will fail to run with the following message:
stdout is not a tty
There are two things you can do.
The quick an easy way is to change the line
at the top of smalltemplate from:
#!/usr/bin/env luajit
to:
#!/usr/bin/env luajit.exe
This will work, especially if you just need a local install script for your templating.
The other option is to provide an alternate script in your PATH with the following text:
#!/bin/sh
luajit.exe "$@"
Ensure it is executable (which in an MSYS-MinGW environment, it will automatically be with the shebang line). I put my scripts in ~/bin, and ensure the following line is in ~/.bashrc:
export PATH="$HOME/bin:$PATH"
Ensure your shell see it:
$ which luajit
/home/itchychips/bin/luajit
If it does not, and you are on bash, run set +h to forget remembered paths
for execution, and see if the script is seen.
Then, you should be able to run scripts with luajit and redirect the output for more than just smalltemplate.
See these issues for the upstream MinGW-packages and winpty projects:
Easter egg is enabled? false