# Setting build parameters with .properties files

Usually, DITA builds require setting a number of parameters that do not change frequently. You can reference a set of build parameters defined in a .properties file when building output with the dita command. If needed, you can override any parameter by specifying it explicitly as an argument to the dita command.

## About .properties files

A .properties file is a text file that enumerates one or more name-value pairs, one per line, in the format `name = value`. The .properties filename extension is customarily used, but is not required.

- Lines beginning with the `#` character are comments.
- Properties specified as arguments of the dita command override those set in .properties files.
  Restriction:
  For this reason, args.input and transtype can’t be set in the .properties file.
- If you specify the same property more than once, the last instance is used.
- Properties not used by the selected transformation type are ignored.
- Properties can reference other property values defined elsewhere in the .properties file or passed by the dita command. Use the Ant `${property.name}` syntax.
- You can set properties not only for the default DITA-OT transformation types, but also for custom plugins.

## Procedure

1. Create your .properties file.
   Tip:
   Copy dita-ot-dir/docsrc/samples/properties/template.properties; this template describes each of the properties you can set.

   For example:

       # Directory that contains the custom .css file:
       args.cssroot = ${args.input.dir}/css/

       # Custom .css file used to style output:
       args.css = style.css

       # Copy the custom .css file to the output directory:
       args.copycss = yes

       # Location of the copied .css file relative to the output:
       args.csspath = branding

       # Generate a full navigation TOC in topic pages:
       nav-toc = full

2. Reference your .properties file with the dita command when building your output.

       dita --input=my.ditamap --format=html5 --propertyfile=my.properties

3. If needed, pass additional arguments to the dita command to override specific build parameters.

   For example, to build output once with `<draft>` and `<required-cleanup>` content:

       dita --input=my.ditamap --format=html5 --propertyfile=my.properties \
            --args.draft=yes

   Tip:
   If you are building in different environments where the location of the input files is not consistent, set args.input.dir with the dita command and reference its value with `${args.input.dir}` in your .properties file.