x
Execute—executing les or changing to the directory
s
Setuid bit—the application or program is started as if it were started by the
owner of the le
As an alternative, a numeric code can be used. The four digits of this code are
composed of the sum of the values 4, 2, and 1—the decimal result of a binary
mask. The rst digit sets the set user ID (SUID) (4), the set group ID (2), and the
sticky (1) bits. The second digit denes the permissions of the owner of the le.
The third digit denes the permissions of the group members and the last digit
sets the permissions for all other users. The read permission is set with 4, the
write permission with 2, and the permission for executing a le is set with 1. The
owner of a le would usually receive a 6 or a 7 for executable les.
gzip [parameters] files
This program compresses the contents of les using complex mathematical algo-
rithms. Files compressed in this way are given the extension .gz and need to be
uncompressed before they can be used. To compress several les or even entire
directories, use the tar command.
-d
Decompresses the packed gzip les so they return to their original size and
can be processed normally (like the command gunzip)
tar options archive files
tar puts one or more les into an archive. Compression is optional. tar is a quite
complex command with a number of options available. The most frequently used
options are:
-f
Writes the output to a le and not to the screen as is usually the case
-c
Creates a new tar archive
-r
Adds les to an existing archive
-t
Outputs the contents of an archive
-u
Adds les, but only if they are newer than the les already contained in the
archive
-x
Unpacks les from an archive (extraction)
Shell Basics 217
