Help with Automobile Database Script

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1. The problem statement, all variables and given/known data:
   Maintain automobile records in a database

Write a shell script to create, view and modify a simple database that contains automobile records. The shell script has to be done in Bourne shell syntax (bash as a matter of fact). You may use all features of bash and any Unix command (in the version that is available on your personal Linux system or turing and hopper). The name of your script is formed from your Z-id followed by ".db". For example, if your Z-id is "z123456" then your script must be called "z123456.db".
The first parameter is always the database being queried. The second parameter is always the command that will be executed. Any parameters that follow are specific to the command that was issued.
The general syntax of script invocation is:
z123456.db dbname command param1 ... paramN
where:

• dbname is the name of the file that contains the database records
• command is one of: new, add, show or delete
• param1 ... paramN are parameters to the specified command

Description of commands and parameters

• new "title text"
  creates a new database with name dbname. The text following the new command will become the first line in the database file. If no text is given, the default is "Automobile Database".
  An error occurs if the database already exists.
  Upon success, the new command reports "New database created".
• add make model year color
  adds a new record to the database. 4 parameters must be listed in this order: make, model, year, color.
  The year must be a 4 digit number greater than 1870 and smaller than 2020. The other parameters are strings.
  Upon success, the add command reports "Successfully added a record to the database".
• show all
  show single number
  show range number1 number2
  allows the user to view all records, just a single record or a range of records in the database. To show a single record the record number is specified after the keyword "single". To show a range of records the 2 numbers after the keyword "range" indicate the start and the end of the range, they are inclusive. The second number must be larger than the first.
  The output of the show command lists records in the database. The first line of output always is the title text from the database. Then follow the lines for the requested entries in the database, either all, a single line, or a range.
  An example "show all" output looks like this: Automobile Database
  Ford, Mustang, 2008, blue with white stripes
  Mitsubishi, Lancer, 2009, white
  Toyota, Camry LE, 2004, black
  Porsche, Cayenne S, 2007, red An example "show range 2 3" output looks like this: Automobile Database
  Mitsubishi, Lancer, 2009, white
  Toyota, Camry LE, 2004, black
• delete all
  delete single number
  delete range number1 number2
  allows the user to delete records: either all, just a single record or a range of records. To delete a single record the record number is specified after the keyword "single". To delete a range of records the 2 numbers after the keyword "range" indicate the start and the end of the range, they are inclusive. The second number must be larger than the first.
  The delete command reports the number of lines deleted, such as "Successfully deleted 4 records from the database". Note that the title line in the database is never deleted.

Error checking

If an an error occurs, print an error message and exit the script. Specifically your script should:

• ensure that the command is spelled correctly
• ensure that all required parameters to the appropriate command are present
• ensure that line numbers fall within the lines present in the database file
• ensure that the database file exists and is readable, and in the case of "add" and "delete" also writable
• if the file is empty (ie. no records), your script should print out a message that no records are found

Database file format

The first line in the database file contains the title text specified in the "new" command. The remaining lines specify automobile entries with fields that are separated by ", ". For example, the database file for the above "show all" command would contain:
Automobile Database
Ford, Mustang, 2008, blue with white stripes
Mitsubishi, Lancer, 2009, white
Toyota, Camry LE, 2004, black
Porsche, Cayenne S, 2007, red

2. Relevant commands, code, scripts, algorithms:
   An example run:
   % ./z123456.db DB new "Example for Assignment"
   New database created
   % ./z123456.db DB add Ford Mustang 2008 "blue with white stripes"
   Successfully added a record to the database
   % ./z123456.db DB add Mitsubishi Lancer 2009 white
   Successfully added a record to the database
   % ./z123456.db DB add Toyota "Camry LE" 2004 black
   Successfully added a record to the database
   % ./z123456.db DB add Porsche "Cayenne S" 2007 red
   Successfully added a record to the database
   % ./z123456.db DB show all
   Example for Assignment
   Ford, Mustang, 2008, blue with white stripes
   Mitsubishi, Lancer, 2009, white
   Toyota, Camry LE, 2004, black
   Porsche, Cayenne S, 2007, red
   % ./z123456.db DB delete single 2
   1 record deleted
   % ./z123456.db DB show all
   Example for Assignment
   Ford, Mustang, 2008, blue with white stripes
   Toyota, Camry LE, 2004, black
   Porsche, Cayenne S, 2007, red
   % cat DB
   Example for Assignment
   Ford, Mustang, 2008, blue with white stripes
   Toyota, Camry LE, 2004, black
   Porsche, Cayenne S, 2007, red

3. The attempts at a solution (include all code and scripts):
   My attempt at this script.

#! /bin/bash

# Assignment 6. Maintain automobile records in a database

# Create a new database
read query
case "$query" in
        new)
                if [ ! -w "$DB" ]; then
                        echo "$DB" > dbname
                else
                echo "Automobile Database" > dbname
                echo "New Database created."
        ;;

# Add make, model, year, color
        add)
                read -p "Enter the make of the car" tmake
                read -p "Enter the model of the car" model
                read -p "Enter the year of the car" year
                read -p "Enter the color of the car" color

                if [ $year =< 1870 $$ => 2020 ]; then
                echo Error with the year. Must be between 1870 and 2020!

                echo Successfully added a record to the database.

        ;;



# Show All

Need help here


# Delete All

and here

4. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number (Link to Course):

Northern Illinois University, Dekalb, Illinois, Raimond Ege, CSCI 330
cs.niu.edu

Note: Without school/professor/course information, you will be banned if you post here! You must complete the entire template (not just parts of it).

Thank you for filling out the form.

Now what is your question? Be more specific than 'need help here'.

Oh sorry. I need help completing the assignment. I am not sure what to do exactly for the Show and Delete areas. As you can see I haven't done much because I am having a bit of trouble.

Well, to show it, you can dump the entire database to the shell by 'cat dbfile'.

Your 'add' section is broken. You don't use <= >= in shell, use -le -ge. $$ won't extend the statement, $$ is a special variable meaning the shell's PID.

Also, you forgot the fi.

Also, your if-statement didn't prevent it from doing anything. Put the error stuff in the if section, the success stuff in the else section.

if [ "$year" -le 1870 ] || [ "$year" -ge 2020 ]
then
...
else
...
fi

And it doesn't add it to the file anyway. echo stuff >> filename to append to the end.

Deleting is not that simple. Lines don't have a 'delete' operation, so deleting it means reading the file out and not printing the lines you want, then replacing the file with the new contents. Were you told any methods like grep for matching and excluding lines from a file?

# Match only the thing you want
grep "thingtomatch" filename > newfile
# Match everything but the pattern
grep -v "thingtoexclude" filename > newfile

Oh ok. I'll work on it using your advice.
and yes we were taught grep.