1 Overview

Xenv reads input files and prints on the standard output their contents, replacing references to the environment variables with their values and shell commands with the output they produce.

It can be used, in particular, in docker containers where using environment variables for configuration became a de-facto standard. This method is obvious when the configuration is consumed by some programming language (PHP, Python or the like). It is difficult, however, to expand environment variables in configuration files of the programs that provide no mechanism for this (such as mysqld or bind, for instance). This is where xenv comes into play.

By default, xenv looks in the input text for the variable references and command invocations in POSIX shell format and expands them, reproducing the rest of the material verbatim. If the shell syntax does not suit well the language or structure of the input, an alternative syntax can be selected from the command line. A number of additional constructs is provided, such as comments, conditional directives, etc. These optional features can be controlled from the command line as well.