Due 10 October 2015 Noon

The easiest way to create and edit these is to put them in a text file. You can then source this file to declare or redefine the aliases and functions in the current login shell. If you named the file assn04, you can initialize them with the command sequence :

. assn04

The source command will read each line of the file and enter it into the command line buffer as if you were typing it in yourself.

The aliases and functions will now be loaded into your current login shell. Test your aliases and functions. If you find mistakes, simply edit your "assn04" file, fix your mistakes, save, and source the file again.

To prepare for this assignment, do the following.

Read the lectures on the command line and delimiters, variables, and functions.

Read the man pages on the following entries :

Read the man page and book on the test command.
Read the man page and book on the find command.
Read the man page and book on the tr command.
Read the man page and book on the date command.
Read the man page and book on the strftime command.

Give the problem number, a general description ( you don't have to copy the problem verbatim ) and any comments to help yourself.

To figure out what comments to use, pretend that you were going to be a TA next year for this course and that you were going to use your assignment as a key to counsel any students asking for help. How would you describe your answers so you could understand it after a year.

When creating a function, if possible use the environmental and local variables instead of specific values to make the functions portable.

For example, if you need to access your home directory, use the variable $HOME instead of /home/hopper/your_z9. This will allow your ta to test your functions in her/his account.

Be careful to notice whether the function or alias has caps in its name.

Write the following simple aliases.

1.(2) Write a alias called tstamp that returns the current time as a string of digits consisting of the year, the day of the year, the hour of the day, the minute of the day, and the seconds. See the date man pages for correct options. Choose an option set that generates a single string of digits( numbers ) with no white-space but with all digits, so a 4 digit year, a 3 digit day of the year, hours as 2 digits in 24 hour units, and minutes and seconds as 00-59.

2.(2) Write a alias called fchk that uses test to confirm that the filename specified references a regular file.

3.(2) Write a alias called schk that uses test to confirm that the filename specified is symbolic file.

4.(2) Write a alias called dchk that uses test to confirm that the filename specified is directory file.

5.(2) Write a alias called cchk that uses test to confirm that the filename specified is character special file.

6.(2) Write a alias called bchk that uses test to confirm that the filename specified is block special file.

7.(2) Write a alias called rchk that uses test to confirm that the filename specified references a readable file.

8.(2) Write a alias called echk that uses test to confirm that the file exists. Note : symbolic filename linked to nothing will return false. That is OK.

9.(4) Write an aliasa that prompts the user for a starting directory, then prompts the user for the file to find.

Once it has both, run find starting in the specified directory looking for the file given. Redirect any errors to /dev/null.

Use echo -n to surpress line feed after prompting. And the bash read command to get input.

1. (8 points) Write a function called findit that uses find to search from the directory specified as the 1st argument on the command line and looks for the file specified as the 2nd argument on the command line. Redirect redirect any errors to /dev/null.

Before findit runs find, have it check that the 1st argument exists on the command line.

Use either test's string check for non-zero length. Or you can check that $# variable is greater than zero. $# is the number of arguments passed to a command or function.

If no argument, print an error message.

If 1st argument exists, then check that it represents a directory. If not, print an error message.

Otherwise, run the find.

Pseudo code.

if 1st exists on command line ($1)
then
  if 1st argument is an actual directory name
  then
    run find to look for file named in 2nd command line argument 
      starting in directory specified in 1st argument.
  else
    print error about not a directory
  endif

else  
  print error about missing an argument
endif.

So What should recognize regular, directory, character special, or block special.

If filetype is not one of those, What should check to see if it does exist anyway and report that. If the file does not exist, report that.

It should also recognize if the filename is a symbolic link that is not linked to an actual file. Most of the test commands will follow a symbolic link to the actual file named before testing its existence and type.

Pseudo code guideline :

  if filename is symbolic link
    print message about symbolic link
  endif

  if file is a directory
    print message about directory

  else if file is character special file
    print message about character special

  else if file is block special file
    print message about block special

  else if file is regular file
    print message about regular special
 
  else if file exists
    print message that file exists but is unrecognized.

  else
    print message that there is no file.
 
  end if

The above logic order is a suggestion. Keep in mind that the order of the tests can simplify the logic.

To test What:

Run it on your own assn04 file.
Create a symbolic link to assn04 and test it on the symbolic name.
Create a symbolic link to a non-existent filename and test it on the symbolic name.
Test it on . ( current directory )
Test it on /dev/tty1 - which is a character special file
Test it on a non-existent filename.

Create a directory called junk under your home directory. Make it fully accessible (rwx) only to you the user. Pseudo code guide

Check that $HOME/junk exists as a directory and is readable, writable,
and executable.

You may use test's -a and -o options to do a single
call of test

If junk not usable, 
Then
  print a single "junk inaccessible" message 
  exit junkit function.

Else
  If file to be deleted exists as a regular file.
  Then
    Check to see if the file has more than one name (hard link count).
    Use ls -l and cut to pull the filename count for the file.
    If link count is > 1
    Then
      notify user
    Endif

    Move the file to $HOME/junk, rename it as you move it.
    Use the tstamp alias to append the time as an extension.

  Else
    Show message that file specified for removal is not a regular file. 
  Endif
Endif

junkit target-file

Make a backup copy of the assn04 file and email the file to me (berezin) on hopper/turing.