Red Hat Enterprise Linux 3: Red Hat Enterprise Linux Step By Step Guide
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# 4.2. Identifying and Working with File Types

If you are new to Linux, you may see certain file types that you do not recognize because of their unfamiliar extension. 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:

## 4.2.1. 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

- `.zip` — a file compressed with ZIP compression, commonly found in MS-DOS applications; most compressed files for Linux use the `gzip` compression, so finding a `.zip` archive for Linux files is rare

For information on working with `bzip2`, `gzip`, and `tar` files, refer to Section 4.3 File Compression and Archiving.

## 4.2.2. 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

## 4.2.3. System Files

- `.conf` — a configuration file; configuration files sometimes use the `.cfg` extension, as well

- `.lock` — a lock file; determines whether a program or device is in use

- `.rpm` — a Red Hat Package Manager file used to install software

## 4.2.4. 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

- `.py` — a Python script

- `.so` — a library file

- `.sh` — a shell script

- `.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 example, 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` displays `ASCII text`, telling you it is a text file. Any file that is designated as a text file should be readable by using the `cat`, `more`, or `less` commands, or by using a text editor such as gedit or `vi`.

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

For more information on helpful commands for reading files, refer to Chapter 3 Shell Prompt Basics.

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