Section 5.4. Executable Files Versus Built-in Commands

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5.4. Executable Files Versus Built-in Commands

Most Linux commands invoke utility programs that are stored in the directory hierarchy. Utilities are stored in files that have execute permission. For example, when you type:

$ ls 

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the shell locates the executable program called "ls," which is typically found in the "/bin" directory, and executes it. The way that the shell finds a utility is described later in this chapter. In addition to its ability to locate and execute utilities, the shell contains several built-in commands, which it recognizes and executes internally. I'll describe two of the most useful ones now: echo and cd.

5.4.1. Displaying Information: echo

The built-in echo command displays its arguments to standard output (Figure 5-4).

Shell Command: echo {arg}*

echo is a built-in shell command that displays all of its arguments to standard output. By default, it appends a newline to the output.

All of the shells we will see contain this built-in function, but you may also invoke the utility called echo (found in /bin) instead. This is sometimes useful, as some arguments and subtle behavior may vary between the different built-ins and it can be confusing if you write scripts in more than one of these shells. We'll look at writing shell scripts shortly.

5.4.2. Changing Directories: cd

The built-in cd command changes the current working directory of the shell to a new location, and was described fully in Chapter 3, "GNU Utilities for Nonprogrammers."