The second command line formats the chmod man page (using the
man command), removes extra back spaces (col -b), and sends the output to the file /tmp/chmod
(erasing the previous /tmp/chmod file, if it exists). The final command results in the following text
being added to the user??™s project file:
I finished the project on Sat Jan 27 13:46:49 PST 2008
Understanding File Permissions
After you??™ve worked with Linux for a while, you are almost sure to get a Permission denied
message. Permissions associated with files and directories in Linux were designed to keep users
from accessing other users??™ private files and to protect important system files.
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Running Commands from the Shell 2
The nine bits assigned to each file for permissions define the access that you and others have to
your file. Permission bits for a regular file appear as -rwxrwxrwx.
For a regular file, a dash appears in front of the nine-bit permissions indicator. Instead
of a dash, you might see a d (for a directory), l (for a link), b (for a character device),
or c (for a character device).
Of the nine-bit permissions, the first three bits apply to the owner??™s permission, the next three
apply to the group assigned to the file, and the last three apply to all others. The r stands for read,
the w stands for write, and the x stands for execute permissions.
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