Attempt to expand env vars in the path for File and RollingFileAppenders

Cargo.toml

@@ -18,8 +18,8 @@ json_format = ["serde_json"]
 toml_format = ["toml"]
 
 console_appender = ["console_writer", "simple_writer", "pattern_encoder"]
-file_appender = ["parking_lot", "simple_writer", "pattern_encoder"]
-rolling_file_appender = ["parking_lot", "simple_writer", "pattern_encoder"]
+file_appender = ["parking_lot", "simple_writer", "pattern_encoder", "regex"]
+rolling_file_appender = ["parking_lot", "simple_writer", "pattern_encoder", "regex"]
 compound_policy = []
 delete_roller = []
 fixed_window_roller = []
@@ -68,6 +68,7 @@ serde_json = { version = "1.0", optional = true }
 serde_yaml = { version = "0.8.4", optional = true }
 toml = { version = "0.5", optional = true }
 parking_lot = { version = "0.10.0", optional = true }
+regex = { version = "1", optional = true }
 
 [target.'cfg(windows)'.dependencies]
 winapi = { version = "0.3", optional = true, features = ["handleapi", "minwindef", "processenv", "winbase", "wincon"] }

src/append/file.rs

@@ -92,8 +92,12 @@ impl FileAppenderBuilder {
     }
 
     /// Consumes the `FileAppenderBuilder`, producing a `FileAppender`.
+    /// The path argument can contain environment variables of the form $ENV{name_here},
+    /// where 'name_here' will be the name of the environment variable that
+    /// will be resolved. Note that if the variable fails to resolve,
+    /// $ENV{name_here} will NOT be replaced in the path.
     pub fn build<P: AsRef<Path>>(self, path: P) -> io::Result<FileAppender> {
-        let path = path.as_ref().to_owned();
+        let path = super::env_util::expand_env_vars(path.as_ref().to_path_buf());
         if let Some(parent) = path.parent() {
             fs::create_dir_all(parent)?;
         }
@@ -122,6 +126,10 @@ impl FileAppenderBuilder {
 /// kind: file
 ///
 /// # The path of the log file. Required.
+/// # The path can contain environment variables of the form $ENV{name_here},
+/// # where 'name_here' will be the name of the environment variable that
+/// # will be resolved. Note that if the variable fails to resolve,
+/// # $ENV{name_here} will NOT be replaced in the path.
 /// path: log/foo.log
 ///
 /// # Specifies if the appender should append to or truncate the log file if it

src/append/mod.rs

@@ -23,6 +23,20 @@ pub mod file;
 #[cfg(feature = "rolling_file_appender")]
 pub mod rolling_file;
 
+#[cfg(any(feature = "file_appender", feature = "rolling_file_appender"))]
+mod env_util {
+    pub fn expand_env_vars(path: std::path::PathBuf) -> std::path::PathBuf {
+        let mut path: String = path.to_string_lossy().into();
+        let matcher = regex::Regex::new(r#"\$ENV\{([\w][\w|\d|\.|_]*)\}"#).unwrap();
+        matcher.captures_iter(&path.clone()).for_each(|c| {
+            if let Ok(s) = std::env::var(&c[1]) {
+                path = path.replace(&c[0], &s);
+            }
+        });
+        path.into()
+    }
+}
+
 /// A trait implemented by log4rs appenders.
 ///
 /// Appenders take a log record and processes them, for example, by writing it

src/append/rolling_file/mod.rs

@@ -250,6 +250,10 @@ impl RollingFileAppenderBuilder {
     }
 
     /// Constructs a `RollingFileAppender`.
+    /// The path argument can contain environment variables of the form $ENV{name_here},
+    /// where 'name_here' will be the name of the environment variable that
+    /// will be resolved. Note that if the variable fails to resolve,
+    /// $ENV{name_here} will NOT be replaced in the path.
     pub fn build<P>(
         self,
         path: P,
@@ -258,9 +262,10 @@ impl RollingFileAppenderBuilder {
     where
         P: AsRef<Path>,
     {
+        let path = super::env_util::expand_env_vars(path.as_ref().to_path_buf());
         let appender = RollingFileAppender {
             writer: Mutex::new(None),
-            path: path.as_ref().to_owned(),
+            path,
             append: self.append,
             encoder: self
                 .encoder
@@ -287,6 +292,10 @@ impl RollingFileAppenderBuilder {
 /// kind: rolling_file
 ///
 /// # The path of the log file. Required.
+/// # The path can contain environment variables of the form $ENV{name_here},
+/// # where 'name_here' will be the name of the environment variable that
+/// # will be resolved. Note that if the variable fails to resolve,
+/// # $ENV{name_here} will NOT be replaced in the path.
 /// path: log/foo.log
 ///
 /// # Specifies if the appender should append to or truncate the log file if it