Shell Script to generat comma seperated output from a file

#!/bin/bash
counter=1
invoice_clause=""
while read line
do
    if [ $count == 1 ]
    then
    #invoice_clause="'$line'"
        echo "if then"
    else
    invoice_clause="$invoice_clause,'$line'"
    fi
    counter=`expr $counter + 1`
done < invoices.num

echo $invoice_clause


Input file :
one
two
three
four
five

Output:
'one','two','three','four','five'

Simple Python script to convert name value to tabular format

#!/usr/bin/env python
import csv

file1reader = csv.reader(open("mapping.csv"), delimiter=",")

header1 = file1reader.next() #header
header2 = file1reader.next() #header

data = dict()
result=[]
row=[]
for Key, Prop, Val, Flag in file1reader:
        if key in data: # found it
        x=data[Key]
        data[Key] = x + "," + Val
        row.append(Val)
    else:
        data[Key] = Val
        result.append(row)
        row=[]
        row.append(Key)
        row.append(Val)
   
with open('myfile.csv', 'wb') as f:
    w = csv.writer(f,dialect='excel')
    w.writerows(result)   

Example mapping.csv file:

Key1, prop1, value1
Key1, prop2, value2
Key1, prop3, value3
Key2, prop1, value4
Key2, prop2, value5
Key2, prop3, value6

Output file:
Key1, value1, value2, value3
Key2, value3, value4, value5

Technical Interview questions

Q: What happens when you enter URL in the browser?
A:
1.    browser checks cache; if requested object is in cache and is fresh, skip to 9
2.    browser asks OS for server's IP address
3.    OS makes a DNS lookup and replies the IP address to the browser
4.    browser opens a TCP connection to server (this step is much more complex with HTTPS)
5.    browser sends the HTTP request through TCP connection
6.    browser receives HTTP response and may close the TCP connection, or reuse it for another request
7.    browser checks if the response is a redirect (3xx result status codes), authorization request (401), error (4xx and 5xx), etc.; these are handled differently from normal responses (2xx)
8.    if cacheable, response is stored in cache
9.    browser decodes response (e.g. if it's gzipped)
10.  browser determines what to do with response (e.g. is it a HTML page, is it an image, is it a sound clip?)
11.  browser renders response, or offers a download dialog for unrecognized types

Q: How to implement queue using stack?
A: hint: To use two stacks

Q: Design a elevator system in a high rise tower
A: Hint: Use elevation and speed parameters to control stopping of elevator at specific floor.

Q: How to implement a HashMap, what are methods to override?
A: Hint : Override equals, hashCode method of object class
Main methods to implement are put and get

Q: What is dependency injection?
A: Is inject dependency through configuration files - constructor injection, setter injection etc used in spring framework

Q: How spring AOP works?
A: Hint: Uses wrapper (proxy) classes. Another way is to modify byte code but not supported in spring.

Q: How do you keep track of multiple requests on backhand modifying same object?
A: through versions, increment record version in db to avoid race conditions/data courrption

Q: Describe popular design patterns
A: Singleton, Factory (With spring-framwork, you get these out of the box)
visitor, facade, builder, strategy