Due Friday 9 October 2015, 5PM Friday.

What to hand in:

Email the file containing the aliases designed to solve problems described below. Also, bring to class the hard copy.

You are to create a set of aliases that act according to the descriptions listed below.

The easist way to create and edit aliases is to put them in a text file. You can then source this file to assign the aliases to the current login shell.

To source the alias file, create a text file containing the aliases you wish to use. If you named the file myaliases, then to activate the aliases, at the prompt, type:

. myaliases

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. Note the commands must conform to the c-shell command line syntax.

The aliases will now be loaded into your current login shell. Test your aliases. If you find mistakes, simply edit your "myaliases" file, fix your mistakes and save. When you are ready to try the changes, run the source command again on your file and the new version of the aliases defined in the file will be loaded.

You may create intermediate aliases to help with debugging and printout.

To prepare for this assignment, do the following.

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.
Create a directory called junk under your home directory. Make it fully accessable only to you the user.

Put comments in the myaliases file before each alias. Give the problem number, a general description ( you don't have to copy the problem verbatum ) and any comments to help yourself. Put # at the beginning of the comment line. 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 an alias, if possible use the environmental and local variables instead of specific values to make the aliases portable. For example, if you need to access your home directory, use the variable $HOME instead of /usr2/your_z9. This will allow your ta to test your aliases on her/his account.

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

1. Write the following simple aliases.

a.(2) Write an 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, and the minute of the day. See the date and strftime man pages for correct options. Choose an option set that generates a single string of digits( numbers ) with no whitespace.

b.(2) Write an alias called dirchk that uses test to confirm that the filename specified is a directory that is readable, writable and executable. test automatically sets the status depending on the results of the particular test. Remember status is checked by && and || and can be used to control further action of an alias.

c.(2) Write an alias called rfilechk that uses test to confirm that the filename specified references a regular file that is readable and writable.

This problem is best done by combining several small aliases.

a.(5) Using the test command, write one alias for each of the test condition(s) below. If the test that the alias runs is true, it should print the filename passed to it and a message stating what was found.
• Filename refers to a regular file
• Filename refers to a directory file
• Filename refers to a some other filetype (it exists)
• Filename is a symbolic link

Also create an alias that displays the message File does not exist

Possible names for these aliases are rmsg, dmsg, omsg, smsg, and emsg. You can make up your own names, but try to keep them under 6 characters long.

b.(8) Combining the aliases above, What should be able to take the first argument on the command line as the filename to examine and report what it actually is. It should peform the following logic to do this.

If the filename is a symbolic filename.

print the appropriate message

If the filename or link refers to a regular file

print the appropriate message

Else if the filename or link refers to a directory file
print the appropriate message

Else if the filename or link does exist but refers to some other filetype.
print the appropriate message

Else if the filename does not exist even if the symbolic link file does.
print the appropriate message

To test What:

Run it on your own myaliases file.
Create a symbolic link to myaliases and test it on the symbolic name.
Create a symbolic link to a non-existant filename and test it on the symbolic name.
Test it on . ( current directory )
Test it on /devices/pseudo/mm@0:null - which is a character special file
Test it on a non-existant filename.

The Rm alias must do the following steps. (remember aliases are one line command sequences, DO NOT use the c-shell script code)

Test for the existence of the file as a regular file. (use test)
If it exists as a regular file,

Get the link count of the specified file. If count is 1

delete the file.

Else
Inform user
perform an interactive delete of the file.

Endif

Remember one of the short comings of hard linking was that a file with multiple links is not destroyed until all links are deleted. This alias will warn you if a file may have more names associated with it.

To test for the link count, do a long listing and cut the columns (do at least two columns) containing the link count. If the value in those columns is greater than one, then do the conditional remove after informing the user.

You may want to create two additional aliases. One just to test of the link count of the specified file. And the other to print the message and run the conditional delete.

4.(7) Write an alias called Del that removes a file by moving its hard link to the junk directory under a new name. This new name consists of the name of the original file (discard the path info) and an added extension consisting of a number. The filename supplied to del may include path info which must be removed when copied to junk. To generate the number for the extension, call the tstamp alias

To run this alias, you must have a directory called junk in your home directory. If it does not exist, create it and make it fully accessable only to you.

You will be using one or more of the aliases created in problem 1.

The Del alias must perform the following actions.

When you test for your junk directory, use $HOME variable for name of the home directory , DON'T hard code path, append junk to the contents of $HOME

If the junk directory is not in user's home directory or is not usable (use dirchk and possibly rearrange the logic).

Quit with an error message "Can't access junk"

If the file specified on the command line is a regular file. (Do not use rfilechk - it tests for more than is required for a move)
Move the original filename to junk directory while appending the number generated by tstamp.

else
print error "can't back up"
endif

The filename specified may be path qualfied, so you will have to use the history mechanism to slice and dice.

5.(6) Write an alias called capit that converts all the letters in lower case to upper case. Use tr to translate characters. Because tr creates a new file, you need to do the following.

(Note in the following, "original" represents the name specified as the first argument of the alias, Do not hard code the word "original" in the alias )

Use rfilechk to check that "original" is a regular file and accessable.
If accessable regular file

Translate the file to upper case and name the new file with the same name as "original" but append the current process id as an extension to it.

If translate is successful,

rename original to original.old

If rename is successful,

rename original.(process id) to original

endif
endif

6.(6) Write an alias 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 find's output to to the screen, pausing between screens. However, redirect any error messages to /dev/null

7.(6) Write an alias called dups that finds the inode of the file specified as the 2nd argument on the command line and looks for any other filenames linked to the same inode number. The 1st argument on the command line is to specify the directory it is to start looking in. If a match is found, offer to delete it. (see the -ok option of find)

To simplify the dups alias, create an alias called cutit that gets the inode of the specified file. Make dups invoke cutit when you need the inode id.