Exercises
=========

Download the :download:`files <exercise_ult.tar.gz>` required for these execrises.


Self Exercises (Not to be submitted)
------------------------------------

1. Login to your machine from the CLI prompt, by pressing Ctrl+Alt+F1. 

#. Logout and re-login. 

#. What is your present working directory, once you login?

#. List all the files present in your current working directory. 

#. Navigate to the ``Desktop`` directory. If such a directory is not
   present create one.

#. Navigate back to the ``home`` directory. 

#. Create a directory called ``ult`` inside another directory called
   ``sees``. Create both the directories in a single command.

#. What would be your present working directory after doing the
   following?

   ::
   
       cd ~/sees/./../

#. Use the touch command to create a file with your name in the
   ``ult`` folder.

#. Remove the file you created in the previous step. 

#. Navigate to your home directory and remove the directory
   ``sees``. Use ``rm`` command.

#. Re-create the directories ``sees`` and ``ult`` again. Now, remove
   them using the ``rmdir`` command. Use ``man`` or ``--help``, if
   required.

#. Create a file with your first-name in your home directory and copy
   it to ``sees/ult``.

#. Copy the file again, but this time, ensure that ``cp`` checks if
   such a file doesn't already exist.

#. Copy the directory ``sees`` to the directory ``sttp``.

#. Rename directory ``sttp`` with your name.

#. Create a file ``test`` and modify its permission for user and group
   to ``execute``.

#. For the same ``test`` file, change mode to ``r,w,x`` for
   all(user,group,others).

#. Change ownership of the file ``test`` to some other user (if exists).

#. Count the number of files (files, sub-directories, etc.) in a directory. 

#. Create a new file ``alice.txt`` by concatenating the first 30 lines
   and the last 40 lines of ``wonderland.txt``.

#. Show the lines from 10 to 20 of ``primes.txt`` 

#. Concatenate the content of ``foo.txt`` and ``bar.txt`` in a single
   ``foobar.txt`` but with the ``source:wikipedia`` line appearing only
   once, at the end of the file. 

For Assessment (assignment to be submitted before Monday, 8th Aug, 8am)
-----------------------------------------------------------------------

0. Read through the section ``REGULAR EXPRESSIONS`` in ``man grep``

#. Read through in ``man expr``

#. grep the marks of the students who scored above 75 in atleast one
   subject. 

#. grep the marks of all the students whose names begin with an 's'

#. grep the marks of all the students whose names begin with
   consonants. 

#. change the results.sh script to accept the input files also as
   arguments. 

#. Write a shell script that will take a filename as input and check
   if it is executable. 

#. Modify the script in the previous step, to remove the execute
   permissions, if the file is executable. 

#. Write a shell script to remove all executable files from a
   directory, when a directory is given as argument. 

#. List all the years between 2001 and 2099 which have 5 Fridays,
   Saturdays and Sundays in the month of July. Hint: ``man cal``

#. Generate frequency list of all the commands you have used, and show
   the top 5 commands along with their count. (Hint: ``history`` command
   will give you a list of all commands used.)

#. generate a word frequency list for ``wonderland.txt``. Hint: use
   ``grep``, ``tr``, ``sort``, ``uniq`` (or anything else that you want)

#. Print the middle line of the file ``wonderland.txt``. 

#. Write a code that lists the last word of the string in one file and remaining string in another file.
   E.g.-In "Who is Homer Simpson",'Simpson' should be written in one file and 'Who is Homer' should
   be written in another file.

#. Write a bash script that takes 2 or more arguments,

      * All arguments are filenames
      * If fewer than two arguments are given, print an error message
      * If the files do not exist, print error message
      * Otherwise concatenate files

#. Write a script that takes exactly one argument, a directory name. If the number of arguments is more
   or less than one, print a usage message. If the argument is not a directory, print another message.
   For the given directory, print the five biggest files and the five files that were most recently modified.