Java Reference
In-Depth Information
Filenames are case sensitive—upper- and lowercase names are different.
The files ReadMe.txt and readme.txt could both be in the same directory;
they are distinct files.
Avoid using spaces in filenames, as the shell uses whitespace to delineate
between arguments on a command line. You can put a blank in a name, but
then you always have to put the name in quotes to refer to it in the shell.
To give a filename more visual clues, use a period or an underscore.
You can combine several in one filename, too. The filenames
read_me_before_you_begin or test.data.for_my_program may be
annoyingly long to type, but they are legal filenames.
NOTE
The period, or “dot,” in Linux filenames has no special meaning. If you come
from the MS-DOS world, you may think of the period as separating the filename
from the extension, as in myprogrm.bas where the filename is limited to eight
characters and the extension to three characters. Not so in Linux. There is no
“extension,” it's all just part of the filename.
You will still see names like delim.c or Account.java , but the .c or
.java are simply the last two characters or the last five characters, respective-
ly, of the filenames. That said, certain programs will insist on those endings for
their files. The Java compiler will insist that its source files end in .java and
will produce files that end in .class —but there is no special part of the file-
name to hold this. This will prove to be very handy, both when you name your
files and when you use patterns to search for files (see below).
1.3.4
Permissions in Linux are divided into three categories: the owner of a file
(usually the user who created it), the group (a collection of users), and others ,
meaning everyone who is not the owner and not in the group. Any file belongs
to a single owner and, simultaneously, to a single group. It has separate
read/write/execute permissions for its owner, its group, and all others. If you
are the owner of a file, but also a member of the group that owns the file, then
the owner permissions are what counts. If you're not the owner, but a member
of the group, then the group permissions will control your access to the file. All
others get the “other” permissions.
If you think of the three permissions, read/write/execute, as three bits of
a binary number, then a permission can be expressed as an octal digit—where
the most significant bit represents read permission, the middle bit is write
Permissions
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