diff --git a/src/main.rs b/src/main.rs
index cdb7335..9b12ba9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -299,6 +299,8 @@ fn run_one(
     let mut user_env: Vec<(String, String)> = vec![];
     let mut setup_commands: Vec<Command> = vec![];
     let mut teardown_commands: Vec<Command> = parsed.teardown_commands.clone();
+    let mut setup_defs: Vec<(String, String)> = vec![];
+    let mut user_defs: Vec<(String, String)> = vec![];
 
     for d in &parsed.directives {
         match d {
@@ -322,8 +324,14 @@ fn run_one(
                     }
                 };
                 for sd in &setup_parsed.directives {
-                    if let Directive::Env { key, value, .. } = sd {
-                        setup_env.push((key.clone(), value.clone()));
+                    match sd {
+                        Directive::Env { key, value, .. } => {
+                            setup_env.push((key.clone(), value.clone()));
+                        }
+                        Directive::Def { name, body, .. } => {
+                            setup_defs.push((name.clone(), body.clone()));
+                        }
+                        _ => {}
                     }
                 }
                 setup_commands.extend(setup_parsed.commands);
@@ -332,9 +340,21 @@ fn run_one(
             Directive::Env { key, value, .. } => {
                 user_env.push((key.clone(), value.clone()));
             }
+            Directive::Def { name, body, .. } => {
+                user_defs.push((name.clone(), body.clone()));
+            }
         }
     }
 
+    // Merge defs: setup first, then user overrides
+    let mut defs: std::collections::HashMap<String, String> = std::collections::HashMap::new();
+    for (name, body) in &setup_defs {
+        defs.insert(name.clone(), body.clone());
+    }
+    for (name, body) in &user_defs {
+        defs.insert(name.clone(), body.clone());
+    }
+
     // Merge env: setup first, then user overrides
     let mut env_vars: Vec<(String, String)> = vec![];
     env_vars.extend(setup_env.clone());
@@ -349,10 +369,22 @@ fn run_one(
         env_vars.push(("PORT".to_string(), port.to_string()));
     }
 
+    // Apply macro substitutions
+    let apply_defs = |commands: &mut Vec<Command>| {
+        for cmd in commands.iter_mut() {
+            if let Some(body) = defs.get(&cmd.command) {
+                cmd.command = body.clone();
+            }
+        }
+    };
+    let mut user_commands = parsed.commands.clone();
+    apply_defs(&mut setup_commands);
+    apply_defs(&mut user_commands);
+
     // Merge commands: setup + user + teardown
     let mut merged_commands = Vec::new();
     merged_commands.extend(setup_commands.clone());
-    merged_commands.extend(parsed.commands.clone());
+    merged_commands.extend(user_commands.clone());
     merged_commands.extend(teardown_commands.clone());
 
     let merged = ShoutFile {
@@ -363,7 +395,7 @@ fn run_one(
     };
 
     let setup_len = setup_commands.len();
-    let user_len = parsed.commands.len();
+    let user_len = user_commands.len();
 
     let run_opts = RunOptions {
         clean_env: opts.clean_env,
diff --git a/src/parse.rs b/src/parse.rs
index c617f22..84d14c0 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -25,6 +25,7 @@ pub enum ExitCode {
 pub enum Directive {
     Setup { path: String, line: usize },
     Env { key: String, value: String, line: usize },
+    Def { name: String, body: String, line: usize },
 }
 
 #[derive(Debug, Clone)]
@@ -109,6 +110,29 @@ fn parse_env_directive(path: &str, line: &str, line_num: usize) -> Result<(Strin
     }
 }
 
+/// Parse `@def name body` with backslash continuation support.
+/// Returns (name, body, number_of_lines_consumed).
+fn parse_def_directive(path: &str, rest: &str, line_num: usize, lines: &[&str]) -> Result<(String, String, usize), ParseError> {
+    let rest = rest.trim();
+    let space = rest.find(' ').ok_or_else(|| {
+        ParseError(format!("{}:{}: @def requires a name and body", path, line_num))
+    })?;
+    let name = rest[..space].to_string();
+    let mut body = rest[space + 1..].to_string();
+    let mut consumed = 1;
+
+    // Handle backslash continuation
+    while body.ends_with('\\') {
+        body.pop(); // remove trailing backslash
+        consumed += 1;
+        if consumed <= lines.len() {
+            body.push_str(lines[consumed - 1].trim_start());
+        }
+    }
+
+    Ok((name, body, consumed))
+}
+
 fn finalize_command(cmd: &mut Command) {
     let trimmed = trim_trailing_empty(&cmd.expected);
     let (expected, exit_code) = parse_exit_code(&trimmed);
@@ -128,10 +152,13 @@ pub fn parse_setup(path: &str, content: &str) -> Result<ShoutFile, ParseError> {
     let mut teardown_commands = Vec::new();
     let mut directives = Vec::new();
 
-    for (i, &line) in raw_lines.iter().enumerate() {
+    let mut i = 0;
+    while i < raw_lines.len() {
+        let line = raw_lines[i];
         let line_num = i + 1;
 
         if line.is_empty() || line.starts_with('#') {
+            i += 1;
             continue;
         }
 
@@ -139,6 +166,11 @@ pub fn parse_setup(path: &str, content: &str) -> Result<ShoutFile, ParseError> {
             let _ = rest; // parsed below
             let (key, value) = parse_env_directive(path, line, line_num)?;
             directives.push(Directive::Env { key, value, line: line_num });
+        } else if let Some(rest) = line.strip_prefix("@def ") {
+            let (name, body, lines_consumed) = parse_def_directive(path, rest, line_num, &raw_lines[i..])?;
+            directives.push(Directive::Def { name, body, line: line_num });
+            i += lines_consumed;
+            continue;
         } else if let Some(rest) = line.strip_prefix("@teardown ") {
             if rest.trim().is_empty() {
                 return Err(ParseError(format!("{}:{}: @teardown requires a command", path, line_num)));
@@ -163,6 +195,7 @@ pub fn parse_setup(path: &str, content: &str) -> Result<ShoutFile, ParseError> {
                 exit_code: ExitCode::Default,
             });
         }
+        i += 1;
     }
 
     Ok(ShoutFile {
@@ -187,7 +220,9 @@ pub fn parse(path: &str, content: &str) -> Result<ShoutFile, ParseError> {
     let mut current: Option<Command> = None;
     let mut seen_command = false;
 
-    for (i, &line) in raw_lines.iter().enumerate() {
+    let mut i = 0;
+    while i < raw_lines.len() {
+        let line = raw_lines[i];
         let line_num = i + 1;
 
         // Directives (before first command)
@@ -198,6 +233,11 @@ pub fn parse(path: &str, content: &str) -> Result<ShoutFile, ParseError> {
                     return Err(ParseError(format!("{}:{}: @setup requires a file path", path, line_num)));
                 }
                 directives.push(Directive::Setup { path: setup_path.to_string(), line: line_num });
+            } else if let Some(rest) = line.strip_prefix("@def ") {
+                let (name, body, lines_consumed) = parse_def_directive(path, rest, line_num, &raw_lines[i..])?;
+                directives.push(Directive::Def { name, body, line: line_num });
+                i += lines_consumed;
+                continue;
             } else if let Some(rest) = line.strip_prefix("@teardown ") {
                 if rest.trim().is_empty() {
                     return Err(ParseError(format!("{}:{}: @teardown requires a command", path, line_num)));
@@ -215,6 +255,7 @@ pub fn parse(path: &str, content: &str) -> Result<ShoutFile, ParseError> {
             } else {
                 return Err(ParseError(format!("{}:{}: unknown directive: {}", path, line_num, line)));
             }
+            i += 1;
             continue;
         }
 
@@ -244,6 +285,7 @@ pub fn parse(path: &str, content: &str) -> Result<ShoutFile, ParseError> {
         } else if let Some(ref mut cmd) = current {
             cmd.expected.push(line.to_string());
         }
+        i += 1;
     }
 
     if let Some(ref mut cmd) = current {