In Unix, filenames can generally be up to 255 characters long and contain any character except / and nul
However just because you can use most any character, it doesn't mean it's a good idea to do so.
Also in general, filenames are case sensitive, e.g the following two files are different.
You can also use multiple .'s in filenames. e.g it is quite common to see something like
Unix doesn't really have the filename extension concept that Windows does. It is more a convention. As such, you aren't restricted to three characters for the extension, you don't even need one or you can use more e.g
file file.jpeg file.html
It is all too common to see files with spaces in their name e.g
My Document.txtAt first glance this may seem fairly innocuous. However this is a common source of problems when working from the shell. When working with such files you need to generally do one of two things Quote the filename
'My Document.txt'or escape the space
My\ Document.txtThis gets tired real quick. There are a host of other characters that can cause similar issues, including &, ! and '
The solution is simple, stick to a small subset of the allowed characters.
POSIX even defines such a set here.
It boils down to
I would also suggest to just stick to lower case (unless there's a good reason for upper). Also avoid starting names with a -