Add the 'unset' built-in command

Add the 'unset' command to remove global environment variable
definitions from the shell.

2 files changed, 19 insertions, 1 deletions

diff --git a/src/poem/anthology.rs b/src/poem/anthology.rs
index 94b5f6b..2a2f62a 100644
--- a/src/poem/anthology.rs
+++ b/src/poem/anthology.rs
@@ -7,7 +7,9 @@ use crate::compose::Environment;
 use crate::poem::Verse;
 
 /// A static list of all the built-in commands
-static INDEX: [&str; 6] = ["alias", "cd", "exit", "export", "source", "unalias"];
+static INDEX: [&str; 7] = [
+    "alias", "cd", "exit", "export", "source", "unalias", "unset",
+];
 
 /// Lookup the index of a built-in command
 ///
@@ -30,6 +32,7 @@ pub fn incant(verse: &Verse, index: usize, env: &mut Environment) -> i32 {
         "export" => export::incant(verse),
         "source" => source::incant(verse, env),
         "unalias" => alias::unincant(verse, &mut env.aliases),
+        "unset" => export::unincant(verse),
         _ => unreachable!(),
     }
 }
diff --git a/src/poem/anthology/export.rs b/src/poem/anthology/export.rs
index 76dfd99..a61935c 100644
--- a/src/poem/anthology/export.rs
+++ b/src/poem/anthology/export.rs
@@ -21,3 +21,18 @@ pub fn incant(verse: &Verse) -> i32 {
 
     0
 }
+
+pub fn unincant(verse: &Verse) -> i32 {
+    match verse.clause() {
+        Some(clause) => {
+            for stanza in clause {
+                env::remove_var(stanza);
+            }
+        }
+        None => {
+            eprintln!("unset: not enough arguments");
+            return 1;
+        }
+    }
+    0
+}