EECS 2031 - Lab 4

This question is a continuation of the Lab 3 question. You can continue working with the script you submitted for Lab 3, or use the posted solution. The background section below is the same as for Lab 3 but is copied here for your convenience. Similarly, the Lab 3 requirements are also part of this question. Concentrate on the section entitled Lab 4 requirements.

Background

In many computer science and engineering research projects, researchers are working with information about a set of entities and the relations between them. For instance, the set of entities may be the set of classes in a software system, and the relations may be inheritance, aggregation etc.

A simple way to store such information is in a text file, where each line has the following format:

relation someEntity anotherEntity

There is a single SPACE character separating the three tokens in each line. We can assume that the names of all relations and entities do not contain any spaces. There are no spaces before the relation name, or after the name of the second entity. You can download an example of such a file here.

Your task for this lab exercise, is to create a shell script that works with such a file (see the Requirements section below).

What to do

Create a shell script called lab4.sh in your favourite editor so that it implements the functionality described in the Requirements section below.
Test that your shell script correctly implements the required functionality.
Submit your solution electronically before midnight on Tuesday using the command
```
  submit 2031 Lab4 lab4.sh
```
You may submit your solution more than once. Additional documentation about the submit command can be viewed by typing man submit.

Lab 3 Requirements

Your script will receive no arguments. The first task of your script is to present a prompt to its user. For historical reasons, the prompt will be

Grock-

There should be a space after the dash. To allow the user to enter commands in the same line as the prompt, use printf instead of echo (look up the man page for printf for more information).

For this lab exercise, there are only two commands your script must handle. If any other command is entered, the script should reply

Unrecognized command.

and then present the prompt again. The two commands are:

quit - The script must exit.
setdb inputfile.txt
If inputfile.txt exists, and is readable, then your script must respond with
```
Database set to inputfile.txt
```
The name of the input file may be different of course. In fact, it may be a full path name, such as /cse/home/bil/input.txt

If the input file does not exist, your script must respond
```
File inputfile.txt does not exist.
```
If the input file exists, but is not readable, your script must respond
```
File inputfile.txt is not readable.
```
If no input file is provided, your script must respond
```
Missing Argument.
```
If more than one input file is provided, your script must respond
```
Database set to inputfile.txt
Extra arguments ignored.
```

Following is a sample run that shows the expected behaviour of the script.


% lab3.sh
Grock- goodbye
Unrecognized command.
Grock- setdbb input.txt
Unrecognized command.
Grock- setdb nonexistant.txt
File nonexistant.txt does not exist.
Grock- setdb unreadable.txt
File unreadable.txt is not readable.
Grock- setdb input.txt
Database set to input.txt
Grock- setdb nonexistant.txt input.txt
File nonexistant.txt does not exist.
Extra arguments ignored.
Grock- setdb unreadable.txt input.txt
File unreadable.txt is not readable.
Extra arguments ignored.
Grock- setdb input.txt unreadable.txt
Database set to input.txt
Extra arguments ignored.
Grock- quit
%

Lab 4 requirements

The first requirement for Lab 4 was a bonus question in Lab 3. If you have completed it already, you can skip this part.

Lab 3 bonus question

If the format in the provided file to setdb is not as specified in the Background section, your script must respond as in the following sample run:


% lab4.sh
Grock- setdb badformat.txt
Incorrect format in badformat.txt.
The following lines were incorrectly formatted.
d d d d
 dfsdfg afegsdfh asfg
efgfah afgadfg adfsg 
awg  awg wga
wrhg warg  wrgrw
awdg afsg
sdg

asdg asdg asdg asdg
Database not set.
Grock- quit
%

Additional requirements

Implement a new command called relnames that prints the name of all relations in the database file. If the database has not been set, it should print Database has not been set. See the sample run below:
```
% lab4.sh
Grock- relnames
Database has not been set.
Grock- setdb example.txt
Database set to example.txt
Grock- relnames
aggregate
implement
inherit
Grock- quit
%
```
Implement a new command called entities that prints the name of all entities in the database file. If the database has not been set, it should print Database has not been set. Hint: You might find the Unix utility tr useful. See the sample run below:
```
% lab4.sh
Grock- entities
Database has not been set.
Grock- setdb example.txt
Database set to example.txt
Grock- entities
class1
class2
class3
class4
class5
interface1
Grock- quit
% 
```
Implement a new command called cardinality that takes as an argument names of relations and calculates and outputs how many instances of each relation exist in the database file as in the sample run below. If the database has not been set, it should print Database has not been set. If any of the arguments is not a relation in the database file, an error message as in the sample run must be printed.
```
% lab4.sh
Grock- cardinality aggregate
Database has not been set.
Grock- setdb example.txt
Database set to example.txt
Grock- cardinality aggregate
aggregate 1
Grock- cardinality aggregate inherit implement
aggregate 1
inherit 2
implement 1
Grock- cardinality inherit use implement
inherit 2
Relation use does not exist.
implement 1
Grock- quit
% 
```