EECS 2031 - Lab Test 1

This question is a continuation of the Lab 3 and 4 questions. You will be able to continue working with the script you submitted before, or with the solution posted on the course website. You can find the necessary background, as well as the requirements of the Lab 3 and 4 questions on the previous page. The following assumes you are familiar with Labs 3 and 4.

For this test, you can assume that all database files your script will be tested with will have correct format.

For your convenience, you can download the sample database used in Labs 3 and 4 here.

What to do

Create a shell script called lt1m.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 the end of the lab session using the command
```
  submit 2031 LT1M lt1m.sh
```
You may submit your solution more than once. Additional documentation about the submit command can be viewed by typing man submit.

Requirements

In addition to the commands introduced in Labs 3 and 4, your script must implement the following command:

delrel rel output.txt threshold

The expected behaviour is the following:

If the database has not been set by a successful setdb command, then your script must respond with

Database has not been set.

followed by a new prompt.

If there are less than two arguments, your script must respond with

Missing arguments.

followed by a new prompt.

If the first argument does not correspond to a relation in the database file, your script must respond with

Relation rel does not exist.

followed by a new prompt.

If a file whose name matches the second argument exists already, your script must respond with something like

File output.txt exists. No output created.

followed by a new prompt.

If there are only two arguments, your script must create a new file whose name is the second argument and it contains all lines in the database except for the ones that refer to the relation specified by the first argument. You can assume that your script always has permissions to create the output file. Your script must also output to the standard output a message such as the following

Added 5 lines to file output.txt

If there is a third argument, you can assume that it will always be an integer number. If such an argument exists, your script should create the output file as described above only if the cardinality of the relation is larger than the threshold indicated by the third argument. If the file is not created, your script must output to the standard output a message such as the following

Cardinality of relation rel too small.

Your script must ignore any further arguments to delrel without warning the user.

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


% lt1f.sh
Grock- hello
Unrecognized command.
Grock- setdb
Missing Argument.
Grock- setdbb example.txt
Unrecognized command.
Grock- delrel inherit inheritance.txt
Database has not been set.
Grock- setdb example.txt
Database set to example.txt
Grock- delrel
Missing Arguments.
Grock- delrel inherit
Missing Arguments.
Grock- delrel rel output.txt
Relation rel does not exist.
Grock- delrel inherit output_sample_run.fout
Added 2 lines to file output_sample_run.fout
Grock- delrel inherit output_sample_run.fout
File output_sample_run.fout exists. No output created.
Grock- delrel inherit output.txt 3
Cardinality of relation inherit too small.
Grock- quit
% cat output_sample_run.fout
implement class3 interface1
aggregate class3 class5
%