Builtins
A builtin is a utility (also called a command) that is built into a shell. Each of the three major shells—the Bourne Again, TC, and Z—has its own set of builtins. When it runs a builtin, the shell does not fork a new process. Consequently, builtins run more quickly and can affect the environment of the current shell. Because builtins are used in the same way as utilities, you will not typically be aware of whether a utility is built into the shell or is a stand-alone utility.
The echo
utility is a shell builtin. The shell always executes a shell builtin before trying to find a command/utility with the same name. Refer to “which, whereis ...
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