diff --git a/mod.test.ts b/mod.test.ts
index 2bde4f6..598930b 100644
--- a/mod.test.ts
+++ b/mod.test.ts
@@ -691,6 +691,37 @@ Deno.test("exporting env should modify real environment when something changed v
   }
 });
 
+Deno.test("env should be clean slate when clearEnv is set", async () => {
+  {
+    const text = await $`printenv`.clearEnv().text();
+    assertEquals(text, "");
+  }
+  Deno.env.set("DAX_TVAR", "123");
+  try {
+    const text = await $`deno eval 'console.log("DAX_TVAR: " + Deno.env.get("DAX_TVAR"))'`.clearEnv().text();
+    assertEquals(text, "DAX_TVAR: undefined");
+  } finally {
+    Deno.env.delete("DAX_TVAR");
+  }
+});
+
+Deno.test("clearEnv + exportEnv should not clear out real environment", async () => {
+  Deno.env.set("DAX_TVAR", "123");
+  try {
+    const text =
+      await $`deno eval 'console.log("VAR: " + Deno.env.get("DAX_TVAR") + " VAR2: " + Deno.env.get("DAX_TVAR2"))'`
+        .env("DAX_TVAR2", "shake it shake")
+        .clearEnv()
+        .exportEnv()
+        .text();
+    assertEquals(text, "VAR: undefined VAR2: shake it shake");
+    assertEquals(Deno.env.get("DAX_TVAR2"), "shake it shake");
+  } finally {
+    Deno.env.delete("DAX_TVAR");
+    Deno.env.delete("DAX_TVAR2");
+  }
+});
+
 Deno.test("setting an empty env var", async () => {
   const text = await $`VAR= deno eval 'console.log("VAR: " + Deno.env.get("VAR"))'`.text();
   assertEquals(text, "VAR: ");
diff --git a/src/command.ts b/src/command.ts
index 7b2314e..9969d20 100644
--- a/src/command.ts
+++ b/src/command.ts
@@ -79,6 +79,7 @@ interface CommandBuilderState {
   env: Record<string, string | undefined>;
   commands: Record<string, CommandHandler>;
   cwd: string | undefined;
+  clearEnv: boolean;
   exportEnv: boolean;
   printCommand: boolean;
   printCommandLogger: LoggerTreeBox;
@@ -147,6 +148,7 @@ export class CommandBuilder implements PromiseLike<CommandResult> {
     env: {},
     cwd: undefined,
     commands: { ...builtInCommands },
+    clearEnv: false,
     exportEnv: false,
     printCommand: false,
     printCommandLogger: new LoggerTreeBox(
@@ -176,6 +178,7 @@ export class CommandBuilder implements PromiseLike<CommandResult> {
       env: { ...state.env },
       cwd: state.cwd,
       commands: { ...state.commands },
+      clearEnv: state.clearEnv,
       exportEnv: state.exportEnv,
       printCommand: state.printCommand,
       printCommandLogger: state.printCommandLogger.createChild(),
@@ -454,6 +457,18 @@ export class CommandBuilder implements PromiseLike<CommandResult> {
     });
   }
 
+  /**
+   * Clear environmental variables from parent process.
+   *
+   * Doesn't guarantee that only `env` variables are present, as the OS may
+   * set environmental variables for processes.
+   */
+  clearEnv(value = true): CommandBuilder {
+    return this.#newWithState((state) => {
+      state.clearEnv = value;
+    });
+  }
+
   /**
    * Prints the command text before executing the command.
    *
@@ -742,10 +757,11 @@ export function parseAndSpawnCommand(state: CommandBuilderState) {
         stdin: stdin instanceof ReadableStream ? readerFromStreamReader(stdin.getReader()) : stdin,
         stdout,
         stderr,
-        env: buildEnv(state.env),
+        env: buildEnv(state.env, state.clearEnv),
         commands: state.commands,
         cwd: state.cwd ?? Deno.cwd(),
         exportEnv: state.exportEnv,
+        clearedEnv: state.clearEnv,
         signal,
         fds,
       });
@@ -1083,8 +1099,8 @@ export class CommandResult {
   }
 }
 
-function buildEnv(env: Record<string, string | undefined>) {
-  const result = Deno.env.toObject();
+function buildEnv(env: Record<string, string | undefined>, clearEnv: boolean) {
+  const result = clearEnv ? {} : Deno.env.toObject();
   for (const [key, value] of Object.entries(env)) {
     if (value == null) {
       delete result[key];
diff --git a/src/shell.ts b/src/shell.ts
index 1f36812..4d57dce 100644
--- a/src/shell.ts
+++ b/src/shell.ts
@@ -237,6 +237,41 @@ class ShellEnv implements Env {
   }
 }
 
+/**
+ * Like {@link RealEnv} but any read actions will access values that were only set through it
+ * or return undefined.
+ */
+class RealEnvWriteOnly implements Env {
+  real = new RealEnv();
+  shell = new ShellEnv();
+
+  setCwd(cwd: string) {
+    this.real.setCwd(cwd);
+    this.shell.setCwd(cwd);
+  }
+
+  getCwd() {
+    return this.shell.getCwd();
+  }
+
+  setEnvVar(key: string, value: string | undefined) {
+    this.real.setEnvVar(key, value);
+    this.shell.setEnvVar(key, value);
+  }
+
+  getEnvVar(key: string) {
+    return this.shell.getEnvVar(key);
+  }
+
+  getEnvVars() {
+    return this.shell.getEnvVars();
+  }
+
+  clone(): Env {
+    return cloneEnv(this);
+  }
+}
+
 function initializeEnv(env: Env, opts: ShellEnvOpts) {
   env.setCwd(opts.cwd);
   for (const [key, value] of Object.entries(opts.env)) {
@@ -481,12 +516,13 @@ export interface SpawnOpts {
   commands: Record<string, CommandHandler>;
   cwd: string;
   exportEnv: boolean;
+  clearedEnv: boolean;
   signal: KillSignal;
   fds: StreamFds | undefined;
 }
 
 export async function spawn(list: SequentialList, opts: SpawnOpts) {
-  const env = opts.exportEnv ? new RealEnv() : new ShellEnv();
+  const env = opts.exportEnv ? opts.clearedEnv ? new RealEnvWriteOnly() : new RealEnv() : new ShellEnv();
   initializeEnv(env, opts);
   const context = new Context({
     env,