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CompTIA A+ Certification All-in-One Exam Guide

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NOTE Every operating system has some method to change file

associations. If you want to open Microsoft Office .docx files in LibreOffice

instead of Word, there is always a way to do this.

Changing the extension of a data file does not affect the format of its

contents, but without the proper extension, your operating system won’t

know which program uses it. Figure 15-7 shows a folder with two identical

image files. The one on the right shows a thumbnail because Windows

recognizes this as a JPEG image; the one on the left shows a generic icon

because I deleted the extension. Windows’ GUI doesn’t show file extensions

by default, but macOS and most Linux distros do.

Figure 15-7 What kind of file is the one on the left?

The filename and extension matter when working in the command-line

interface because you need to know what type of file you’re accessing when

you type a command. Typing certain filenames, for example, causes the OS

to run an application or run a series of commands to do stuff. Check out

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