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core/variables.py

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+"""Variable substitution for $VAR/${VAR} and {{var}} templates."""
+
+import os
+import re
+from pathlib import Path
+from typing import Dict
+
+
+def substitute(text: str, variables: Dict[str, str]) -> str:
+    """Replace $VAR and ${VAR} with values from variables dict or env."""
+    if not isinstance(text, str):
+        return text
+
+    pattern = re.compile(r"\$(\w+)|\$\{([^}]+)\}")
+
+    def _replace(match: re.Match[str]) -> str:
+        key = match.group(1) or match.group(2) or ""
+        if key in variables:
+            return str(variables[key])
+        if key == "HOME":
+            return str(Path.home())
+        if key in os.environ:
+            return os.environ[key]
+        return match.group(0)
+
+    return pattern.sub(_replace, text)
+
+
+def substitute_template(text: str, context: Dict[str, str]) -> str:
+    """Replace {{key}} placeholders with values from context dict."""
+    if not isinstance(text, str):
+        return text
+
+    def _replace(match: re.Match[str]) -> str:
+        key = match.group(1).strip()
+        return context.get(key, match.group(0))
+
+    return re.sub(r"\{\{(\w+)\}\}", _replace, text)