rshebang

Shebang

r[shebang.intro] A shebang is an optional line that is typically used in Unix-like systems to specify an interpreter for executing the file.

[!EXAMPLE]

#!/usr/bin/env rustx

fn main() {
    println!("Hello!");
}

r[shebang.syntax]

@root SHEBANG ->
    `#!` !((WHITESPACE | LINE_COMMENT | SHEBANG_BLOCK_COMMENT)* `[`)
    ~LF* (LF | EOF)

SHEBANG_BLOCK_COMMENT ->
    `/*` !(`!` | `*` ![`*` `/`])
      ( SHEBANG_NESTED_BLOCK_COMMENT | (!(`*/` | `/*`) CHAR) )*
    `*/`

SHEBANG_NESTED_BLOCK_COMMENT ->
    `/*`
      ( SHEBANG_NESTED_BLOCK_COMMENT | (!(`*/` | `/*`) CHAR) )*
    `*/`

r[shebang.syntax-description] The shebang starts with the characters #! and extends through the first U+000A (LF) or through EOF if no LF is present. If the #! characters are followed by [ (ignoring any intervening whitespace or non-doc comments), the line is not considered a shebang (to avoid ambiguity with an inner attribute).

[!NOTE] Doc comments are not ignored when determining whether [ follows the #! characters. For example, #! /*! */ [allow(unused)] at the start of a file is a shebang, not an inner attribute, because /*! */ is a doc comment. Likewise, text following #! that resembles an unterminated block comment, as in #!/*, does not cause an error; the line is a shebang.

r[shebang.position] The shebang may appear immediately at the start of the file or after the optional byte order mark.