Debian User Reference Manual
Footnotes

1

While you can use almost anything in a file name, in practice it's a bad idea. You want to avoid any characters that often have special meanings, including: { } ( ) [ ] ' ` " \ / > < | ; ! # & ^ * % @

Also avoid putting spaces in filenames. If you want to separate words in a name, good choices are the period, hyphen, and underscore. You can also capitalize each word, LikeThis.

2

Some people spell it as two words, i.e. "file system". A quick poll of man pages (man -k filesystem, man -k 'file system') reveals about an even split. So I'm spelling it as one word. You can do it however you like. :)

3

There are exceptions: see the chapter on shells.

4

This is why system directories should be put first in the path; this ensures that the system commands will be run in preference to ones of the same name in user bin directories or in the current directory. If non-system programs are searched first, there is a security risk, because there may be non-standard programs with commonly-used names, and you cannot tell what they might do.

5

Many people recommend that the current directory should never be included in your path. You can run commands in the current directory by using ./command

6

The syntax given is for Bourne shell and its descendants. The syntax for C shell and its descendants is setenv PATH $PATH:new_directory

7

The alert user may have noticed that each two bytes of the hexadecimal representation is reversed with respect to the characters they represent. That is because this example was run on a PC, which uses little-endian architecture. The results would be the opposite way round on a big-endian architecture.

8

Successful means terminating with an exit status of 0.

Debian User Reference Manual