Enum Type 

pub enum Type {
    Special,
    Mandatory,
    Elective,
    Extension,
    Substitutive,
}

Types of built-in utilities

Variants

Special

Special built-in

Special built-in utilities are built-ins that are defined in POSIX XCU section 2.15.

They are treated differently from other built-ins. Especially, special built-ins are found in the first stage of command search without the $PATH search and cannot be overridden by functions or external utilities. Many errors in special built-ins force the shell to exit.

Mandatory

Standard utility that can be used without $PATH search

Mandatory built-ins are utilities that are listed in POSIX XCU section 1.7. In POSIX, they are called “intrinsic utilities”.

Like special built-ins, mandatory built-ins are not subject to $PATH in command search; They are always found regardless of whether there is a corresponding external utility in $PATH. However, mandatory built-ins can still be overridden by functions.

We call them “mandatory” because POSIX effectively requires them to be built into the shell.

Elective

Non-portable built-in that can be used without $PATH search

Elective built-ins are built-ins that are listed in step 1b of Command Search and Execution in POSIX XCU section 2.9.1.4. They are very similar to mandatory built-ins, but their behavior is not specified by POSIX, so they are not portable. They cannot be used when the (TODO TBD) option is set.

We call them “elective” because it is up to the shell whether to implement them.

Extension

Non-conforming extension

Extension built-ins are non-conformant extensions to the POSIX shell. Like elective built-ins, they can be executed without $PATH search finding a corresponding external utility. However, since this behavior does not conform to Command Search and Execution in POSIX XCU section 2.9.1.4, they cannot be used when the (TODO TBD) option is set.

Substitutive

Built-in that works like a standalone utility

A substitutive built-in is a built-in that is executed instead of an external utility to minimize invocation overhead. Since a substitutive built-in behaves just as if it were an external utility, it must be found in $PATH in order to be executed.

Trait Implementations

impl Clone for Type

fn clone(&self) -> Type

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Type

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Hash for Type

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Type

fn eq(&self, other: &Type) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Type

impl Eq for Type

impl StructuralPartialEq for Type