Learning the bash Shell, Second Edition

Files

Although arguments to commands aren’t always files, files are the most important types of “things” on any UNIX system. A file can contain any kind of information, and indeed there are different types of files. Three types are by far the most important:

Regular files

Also called text files; these contain readable characters. For example, this book was created from several regular files that contain the text of the book plus human-readable formatting instructions to the troff word processor.

Executable files

Also called programs; these are invoked as commands. Some can’t be read by humans; others—the shell scripts that we’ll examine in this book—are just special text files. The shell itself is a (non-human-readable) executable file called bash.

Directories

These are like folders that contain other files—possibly other directories (called subdirectories).

Directories

Let’s review the most important concepts about directories. The fact that directories can contain other directories leads to a hierarchical structure, more popularly known as a tree, for all files on a UNIX system.

Figure 1.2 shows part of a typical directory tree; rectangles are directories and ovals are regular files.

Figure 1-2. A tree of directories and files

The top of the tree is a directory called root that has no name on the system. ^[6] All files can be named by expressing their location on the system ...