Variables

Learn how variables are resolved when functions execute, including environment inheritance and Runfile-level scope.

Environment variables

Functions inherit the caller environment. Two key variables affect run itself:

• RUN_SHELL — override the default shell for execution. Defaults to sh on Unix/macOS, pwsh (or powershell) on Windows.
• RUN_MCP_OUTPUT_DIR — directory for MCP output files when responses are truncated.

Runfile scope

• Top-level variables declared in a Runfile are visible to all functions.
• Sibling functions are injected into the execution scope, so you can call them by name.

Parameter variables

• Signature parameters become shell variables with matching names once the function starts.
• Legacy positional tokens ($1, $2, $@) remain available for backward compatibility.

Polyglot interpreters

When a function uses a shebang or @shell interpreter, arguments are forwarded positionally into that interpreter:

• Python: sys.argv[1], sys.argv[2], ...
• Node.js: process.argv[2], process.argv[3], ...
• Other interpreters receive the same argv array; defaults are applied before forwarding.

For interpreter selection rules, see Attributes and interpreters. For parameter behaviors, see Arguments.