document zebrad enviroment variables

zebrad/src/commands.rs

@@ -24,6 +24,33 @@ use std::path::PathBuf;
 pub const CONFIG_FILE: &str = "zebrad.toml";
 
 /// Zebrad Subcommands
+///
+/// All subcommands support the following enviroment variables:
+/// - `ZEBRAD_CACHE_DIR`: The directory to store zebra data just as state, blocks, wallet, etc.
+/// - `ZEBRAD_LOG`: Manipulate the log level. Regex is supported.
+/// ## Examples:
+///
+/// Use a custom data directory:
+/// ```
+/// export ZEBRAD_CACHE_DIR="/my/zebra_data_dir"
+/// zebrad start
+/// ```
+///
+/// Output all info messages:
+///
+/// ```
+/// export ZEBRAD_LOG="info"
+/// zebrad start
+/// ```
+///
+/// Output block_verify with trace level and above every 1000 blocks:
+///
+/// ```
+/// export ZEBRAD_LOG="[block_verify{height=Some\(BlockHeight\(.*000\)\)}]=trace"
+/// zebrad start
+/// ```
+///
+/// Note: Log options are processed in this order: verbose flag, command stdout, enviroment variable, config file.
 #[derive(Command, Debug, Options, Runnable)]
 pub enum ZebradCmd {
     /// The `generate` subcommand