allow to override existing env vars (#41)

dotenv/src/iter.rs

@@ -35,6 +35,18 @@ impl<R: Read> Iter<R> {
         Ok(())
     }
 
+    /// A version of [load] that overrides older variables in case of duplicates.
+    pub fn overload(mut self) -> Result<()> {
+        self.remove_bom()?;
+
+        for item in self {
+            let (key, value) = item?;
+            env::set_var(key, value);
+        }
+
+        Ok(())
+    }
+
     fn remove_bom(&mut self) -> Result<()> {
         let buffer = self.lines.buf.fill_buf().map_err(Error::Io)?;
         // https://www.compart.com/en/unicode/U+FEFF

dotenv/src/lib.rs

@@ -181,6 +181,19 @@ pub fn dotenv() -> Result<PathBuf> {
     Ok(path)
 }
 
+/// A version of [dotenv] that overrides existing env vars
+///
+/// # Examples
+/// ```
+/// use dotenvy::overload;
+/// overload().ok();
+/// ```
+pub fn overload() -> Result<PathBuf> {
+    let (path, iter) = Finder::new().find()?;
+    iter.overload()?;
+    Ok(path)
+}
+
 /// Returns an iterator over environment variables.
 ///
 /// # Examples

dotenv/tests/test-overload.rs

@@ -0,0 +1,23 @@
+mod common;
+
+use std::{env, error::Error, result::Result};
+
+use dotenvy::*;
+
+use crate::common::*;
+
+#[test]
+fn test_overload() -> Result<(), Box<dyn Error>> {
+    let dir = tempdir_with_dotenv(
+        "
+var=old
+var=new
+",
+    )?;
+    overload()?;
+    assert_eq!(var("var")?, "new");
+
+    env::set_current_dir(dir.path().parent().unwrap())?;
+    dir.close()?;
+    Ok(())
+}