A command can be one of four different things:
1. An executable program like all those files we saw in /usr/bin. Within this
category, programs can be compiled binaries such as programs written in C and
C++, or programs written in scripting languages such as the shell, perl, python,
ruby, etc.
2. A command built into the shell itself. bash supports a number of commands
internally called shell builtins. The cd command, for example, is a shell builtin.
3. A shell function. A programs get longer and more complex, they become more difficult to design, code, and maintain. As with any large endeavor, it is often useful to break a single, large task into a number of smaller tasks.
4. An alias. Commands that we can define ourselves, built from other commands.
1. An executable program like all those files we saw in /usr/bin. Within this
category, programs can be compiled binaries such as programs written in C and
C++, or programs written in scripting languages such as the shell, perl, python,
ruby, etc.
2. A command built into the shell itself. bash supports a number of commands
internally called shell builtins. The cd command, for example, is a shell builtin.
3. A shell function. A programs get longer and more complex, they become more difficult to design, code, and maintain. As with any large endeavor, it is often useful to break a single, large task into a number of smaller tasks.
4. An alias. Commands that we can define ourselves, built from other commands.