As some of you may know Linux does not use the extension (suffix) of the file to determine the type of it, what it does is to look at the file content.

So you can name your files as you want and Linux will still be able to recognize it.

If you ever need to know the type of a given file, with no suffix, or with the incorrect suffix, use the Linux command file

You should have this command already installed on your Linux, but if not, installing it is really simple.

Debian / Ubuntu

sudo aptitude install file

once installed, you can start guessing the file types.

Example:

$ ls *.txt -l
-rw-r--r-- 1 ggarron ggarron  25511 2007-10-25 17:37 dhclient.txt
-rw-r--r-- 1 ggarron ggarron  77757 2007-11-09 10:48 gammu.txt
-rw-r--r-- 1 ggarron ggarron   1298 2007-11-20 16:46 latex.txt
-rw-r--r-- 1 ggarron ggarron  73823 2007-08-31 11:29 man-iptables.txt
-rw-r--r-- 1 ggarron ggarron 142738 2008-01-02 17:28 nmap.txt
-rw-r--r-- 1 ggarron ggarron   9834 2007-12-13 18:12 picture.txt
-rw-r--r-- 1 ggarron ggarron   1717 2007-07-03 12:55 readme.txt
-rw-r--r-- 1 ggarron ggarron   2468 2007-12-27 16:56 robots.txt
-rw-r--r-- 1 ggarron ggarron    105 2007-08-05 01:34 upgrade_readme.txt

Now apply the file command

$ file *.txt
dhclient.txt:       Non-ISO extended-ASCII English text
gammu.txt:          UTF-8 Unicode Pascal program text
latex.txt:          LaTeX 2e document text
man-iptables.txt:   Non-ISO extended-ASCII English text
nmap.txt:           UTF-8 Unicode English text
picture.txt:        PNG image data, 550 x 53, 8-bit/color RGB, non-interlaced
readme.txt:         ASCII English text, with very long lines, with CRLF line terminators
robots.txt:         ASCII English text
upgrade_readme.txt: ASCII English text, with no line terminators

As you can see picture.txt is a PNG file and not a TXT file, you can also see that there are different types of TXT files, it recognize between Pacal program and LaTeX document, when both are plain text.