Identifying and Working with File Types

If you are new to Linux, you may see files with extensions you do not recognize. A file's extension is the last part of a file's name after the final dot (in the file sneakers.txt, "txt" is that file's extension).

Here is a brief listing of file extensions and their meanings:

Compressed and Archived Files

.bz2 — a file compressed with bzip2
.gz — a file compressed with gzip
.tar — a file archived with tar (short for tape archive), also known as a tar file
.tbz — a tarred and bzipped file
.tgz — a tarred and gzipped file.

For information on working with bzip2, gzip, and tar files, refer to the Section called File Compression and Archiving.

File Formats

.au — an audio file
.gif — a GIF image file
.html/.htm — an HTML file
.jpg — a JPEG image file
.pdf — an electronic image of a document; PDF stands for Portable Document Format
.png — a PNG image file (short for Portable Network Graphic)
.ps — a PostScript file; formatted for printing
.txt — a plain ASCII text file
.wav — an audio file
.xpm — an image file

System Files

.conf — a configuration file
.lock — a lock file; determines whether a program or device is in use
.rpm — a Red Hat Package Manager file used to install software

Programming and Scripting Files

.c — a C program language source code file
.cpp — a C++ program language source code file
.h — a C or C++ program language header file
.o — a program object file
.pl — a Perl script
.so — a library file
.tcl — a TCL script

But file extensions are not always used, or used consistently. So what happens when a file does not have an extension, or the file does not seem to be what the extension says it is supposed to be?

That is when the file command can be helpful.

For instance, you find a file called saturday without an extension. Using the file command, you can tell what type of file it is by typing:

file saturday

In the example, the command file saturday will display ASCII text, telling you it is a text file. Any file that is designated as a text file should be readable using the cat, more, or less commands, or using a text editor.

	Tip
	To learn more about `file`, read the man page by typing `man file`.

For more information on helpful commands for reading files, see Chapter 11.