Homework & Coursework Questions

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1. The problem statement, all variables and given/known data:

The assignment is posted below:

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 Ubuntu system or turing and hopper).
Your shell script must be named "niudb". 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:
niudb dbname command param1 ... paramN

where:

dbname is the name of the file that contains the database records
command is one of: create, add, view or delete
param1 ... paramN are paramemters to the specified command
Description of commands and parameters

create
create title text
creates a new database with name dbname. Any text following the create 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 create command reports "New database created".

add make model year color
adds a new record to the database. Up to 4 parameters can be listed in this order: make, model, year, color. If only 3 parameters are given then the script will prompt for the fourth; if only 2 are given it will prompt for parameter 3 and 4; if only one parameter is given it will prompt for parameters 2 to 4; if no parameters are given then it prompts for all 4.
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".

view
view all
view single number
view range number1 number2
allows the user to view all records, just a single record or a range of records in the database. To view a single record the record number is specified after the keyword "single". To view 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 view 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 "view 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 "view range 2 3" output looks like this: Automobile Database
Mitsubishi, Lancer, 2009, white
Toyota, Camry LE, 2004, black

delete
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

2. Relevant commands, code, scripts, algorithms:

sed, case statements, read and if statements.


3. The attempts at a solution (include all code and scripts):

Code:

#! /bin/bash
# Automobile database

read entry
case "$entry" in

#create

   create|CREATE)

   if [ ! -w "$filename"]Z1604464@students.niu.edu != ""
      echo "$filename" > dbname
   else
      echo "Automobile Database" > dbname
   echo "New database created"

#add

   add|ADD)

   make = $make
   model = $model
   year = $year
   color = $color

   if $make == ""
      read -p "Make of the car: " $make
   if $model == ""
      read -p "Model of the car: " $model
   if $year == ""
      read -p "Year of the car: " $year
   if $color == ""
      read -p "Color of the car: " $color

   if $year < 1870 || $year > 2020
      echo "Erro with $year"

   echo "$make, $model, $year, $color" >> db
   echo "Successfully added a record to the database"

#view
 view|VIEW)

   max=$( wc-l db)
   all:
      cat db
  single:
   if $number > max
      printf "Error"
   sed -ne "1p;$numberp" db
   range:
      if $number > max || $number2 > max || $number > $number2
         printf "Error"
      sed -ne "1p;$number,$number2p" db

#delete

   delete|DELETE)

   max =$( wc-l db)
   all:
      sed -ie '2,$d' db
   single:
      if $number > max
         printf "Error"
      sed -ie "$numberd" db
   range:
      if $number > max || $number2 > max || $number > $number2
         printf "Error"
      sed -ie "number,number2d" db

esac

4. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number (Link to Course):
Northern Illinois University, DeKalb (IL), United States, Raymond Ege, CSCI330


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).

Before starting to work on the logic: there are several syntactical errors in your script-attempt you should correct.

Without guarantee for completeness, use "man bash" and "known good" bash scripts (from this site or the net) to find out:

- how is a "if..then..else...fi"-block constructed?

- how is a "case..esac" constructed?

- are spaces in variable assignments allowed? (i.e. is "x=.." and "x = .." the same?)

- are all control structures properly closed ("(" needs a ")", "'" a closing counterpart, etc.)

Post your rewritten script and we will continue.

bakunin