Introduction to Unix
Homework 5


1. Consider the output from ``ls -l``.  Recall that the very first column in
   the output can be a `d`, a `-` or a `l` depending on if the file object
   is a directory, regular file or symbolic link.  Using the `ls -l`,
   `grep` and `wc` commands in a pipe line sequence , how many ordinary
   files, directories, and link files exist in the /usr/bin directory? You
   will need to use a regular expression in the arguments to the `grep`
   command. How did you obtain your answer? Show the commands used.

2. First, enter the `who` command to see the output displayed.  If a user is
   logged in more than once, there may be multiple entries for that person.
   Now devise a pipeline sequence of commands to display a sorted list of
   people currently logged in with no duplication in names.  Note that you
   will need to first filter the data vertically to show only the first
   column.  See the study guide notes on `awk` for how to filter vertically.
   Show the commands used.

3. Use the `find` command to find any regular files in your home directory
   that have the execute bit set for others.  Note from the study guide that
   the `-perm` option to the `find` command takes a mode argument and that
   the mode (either 001 or o+x) is expressed one of: ``-perm o+x``, 
   ``-perm -o+x`` or ``-perm /o+x``

   You may want to seed the activity by creating a file with execute bit for
   others as follows:

        touch testfile
        chmod o+x testfile
   
   Show the command used.

4. Use the ``crontab -e`` command to schedule the cron facility to run the
   `who` command each day at 2pm for the remainder of October.   Show the
   output from entering the ``crontab -l`` command.  Note from the study
   guide about the EDITOR environment variable.  That will be needed if
   you do not feel comfortable using `vi`.