Implementing checksum into program

[Eiji Takanaka]

Hi there, I was just wondering if someone could point me in the right direction to implement a checksum operation in my little bash-script, i've written =), with assistance from kind-folk from ubuntu forums . (Although i implemented the logging and time-stamp function myself as they prove useful to cross-reference with time-stamps from other programs =P. I'm gathering cksum would be appropriate and i was thinking of trying to implement it on the code=$ line some time after the 000 denomination.

Thus far the program is doing what i want it to...incrementing the first 4 digits of the lot, whilst keeping 000 static. The final part will be to calculate and then append the checksum to the end of the 7-digits, keeping the $code variable so that it will output the final 8 digits to the program and logs in question.

Here is my mini-program =P

#!/bin/bash

for i in {0..9999}; do
code=$(printf "%04d"000 $i)
echo $(date +%H:%M:%S)
echo $(date +%H:%M:%S) >> /home/User/log.txt
echo 'wpa_cli wps_reg A0:00:00:00:00:00' $code
echo 'wpa_cli wps_reg A0:00:00:00:00:00' $code >> /home/User/log.txt
wpa_cli wps_reg 00:00:00:00:00:00 $code
sleep 9

done

I've experimented with cksum and i'm pretty sure thats what i'll be needing its just where to insert it into the code and why, that i could do with a hand with, if possible =).

Cheers guys/gals =)

[r-senior]

Good job with the logging!

What are you creating the checksum from?

[Eiji Takanaka]

Hi senior, thanks yeah, i implemented the logging/date function after reading up some more on bash-scripting =).

O.k so i'm hoping to generate the checksum from the now 7 digits that are assigned to the $code variable. I added three static 0's after the incremented first 4 digits, i.e the program now progresses as follows...

0001000
0002000
0003000

and so on and so forth which is awesome because thats exactly what i wanted it to do.

So basically i now need to use what i believe is called an ean-8 calulator/generator to calculate the 8th digit checksum from the previous 7 digits, which i know are now assigned to $code.

This section i expected to breeze, although reading up i think it might prove somewhat trickier than i first anticipated, haha oh well, learning as i go i guess

Any thoughts? =)

[Eiji Takanaka]

My first thoughts were to call a program, maybe an ean-8 module piping the $code variable into it, & returning it with the checkdigit appended. The returned variable being called $code1. Which is then printed & logged.

[r-senior]

Hmm, unless you know better I don't think cksum does the ean-8 check digit. The algorithm appears to be:

Check Digit Calculation

The EAN-8 check digit is calculated using modulo 10 method. Here outlines the steps to calculate EAN-8 check digit:

From the right to left, start with odd position, assign the odd/even position to each digit.
Sum all digits in odd position and multiply the result by 3.
Sum all digits in even position.
Sum the results of step 3 and step 4.
Divide the result of step 4 by 10. The check digit is the number which adds the remainder to 10.

[Eiji Takanaka]

Yeah i was wrong on cksum. Sadly =). Haha i thought it would be as easy as piping into an allready established program but nooooo.... =P.

What i have found is a perl ean-8 module on the cpan site, and a javascript ean-8 calculator, i procured from a website.

Which would be easiest to implement into my bash-script would you suggest?

Heres the javascript version...obviously the only part of the module i really need is the ean-8 part, it has the algorithm there allready, if i can half-inch it and translate it to bash, is that a feasible work-around? Or is transcribing from java to bash somewhat troublesome would you say?

//Calculates the check digit for an ISBN number.
function ISBN(strISBN)
{
var temp;
var ckDigit
var number = new String();
var digits = new Array( );
var i = 0;

number = strISBN;

while (i < number.length) { //This while statement seperates the string
temp = number.charAt(i); //into characters then turns the characters into
temp=parseInt(temp); //integers. The integers are then put into an array.
digits[i] = temp;
i++; }

//This next line computes a check digit. If modulo 11 produces a remainder then the remainder is subtracted
// from 11, to produce the check digit. When the result equals 10, it is exchanged the the Roman Numeral X.
ckDigit = ( (digits[0] *10) + (digits[1] * 9) + (digits[2] * 8) + (digits[3] * 7) + (digits[4] * 6) + (digits[5] * 5) + (digits[6] * 4) + (digits[7] * 3) + (digits[8] * 2) ) % 11;
if (ckDigit != 0) {
ckDigit = 11 - ckDigit; }

if (ckDigit == 10) {
ckDigit = "X"; }

return ckDigit;
}

//Calculates the check digit for an UCC/EAN-8, UCC/EAN-13 and UCC/EAN-14 number and .
function EAN(strEAN)
{
var temp;
var ckDigit;
var number = new String();
var digits = new Array( );
var i = 0;

number = strEAN;

while (i < number.length) { //This while statement seperates the string
temp = number.charAt(i); //into characters then turns the characters into
temp=parseInt(temp); //integers. The integers are then put into an array.
digits[i] = temp;
i++; }

if (i == 12) { // If i = 13 then calculate a checkdigit for an EAN/UCC-13.

ckDigit = ( (digits[0] + digits[2] + digits[4] + digits[6] + digits[8] + digits[10] ) + ( (digits[1] + digits[3] + digits[5] + digits[7] + digits[9] + digits[11] ) *3) ) % 10;
if (ckDigit != 0) {
ckDigit = 10 - ckDigit; }

return ckDigit; }

if (i == 7) { // If i = 7 then calculate a checkdigit for an EAN/UCC-8.

ckDigit = ( ( (digits[0] + digits[2] + digits[4] + digits[6] ) *3) + ( digits[1] + digits[3] + digits[5] ) ) % 10;
if (ckDigit != 0) {
ckDigit = 10 - ckDigit; }

return ckDigit; }

if (i == 13) { // If i = 13 then calculate a checkdigit for an EAN/UCC-14.

ckDigit = ( ( (digits[0] + digits[2] + digits[4] + digits[6] + digits[8] + digits[10] + digits[12] ) *3) + ( digits[1] + digits[3] + digits[5] + digits[7] + digits[9] + digits[11] ) ) % 10;
if (ckDigit != 0) {
ckDigit = 10 - ckDigit; }

return ckDigit; }
}

//Calculates the check digit for a Bookland EAN number.
//Function receives the ISBN number and "978" is added during the calculation.
function bl_EAN(strISBN)
{
var temp;
var ckDigit;
var number = new String();
var digits = new Array( );
var i = 0;

number = strISBN;

while (i < number.length) { //This while statement seperates the string
temp = number.charAt(i); //into characters then turns the characters into
temp = parseInt(temp); //integers. The integers are then put into an array.
digits[i] = temp;
i++; }

//This next line computes a check digit. If modulo10 produces a remainder then the remainder
// is subtracted from 10, to produce the check digit.

ckDigit = ( (9 + 8 + digits[1] + digits[3] + digits[5] + digits[7] ) + ( (7 + digits[0] + digits[2] + digits[4] + digits[6] + digits[8] ) * 3) ) % 10;
if (ckDigit != 0) {
ckDigit = 10 - ckDigit; }

temp = "978" + digits[0] + digits[1] + digits[2] + digits[3] + digits[4] + digits[5] + digits[6] + digits[7] + digits[8] + ckDigit;
return temp;
}

//Calculates the check digit for a SSCC number.
function SSCC(strSSCC)
{
var temp;
var ckDigit;
var number = new String();
var digits = new Array( );
var i = 0;

number = strSSCC;

while (i <= number.length) { //This while statement seperates the string
temp = number.charAt(i); //into characters then turns the characters into
temp = parseInt(temp); //integers. The integers are then put into an array.
digits[i] = temp;
i++; }

//This next line computes a check digit. If modulo 10 produces a remainder then the remainder
// is subtracted from 10, to produce the check digit.
ckDigit = ( ( (digits[0]+digits[2]+digits[4]+digits[6]+digits[8]+digits[10]+digits[12]+digits[14]+digits[16] ) * 3 ) + (digits[1]+digits[3]+digits[5]+digits[7]+digits[9]+digits[11]+digits[13]+digits[15] ) ) % 10;
if (ckDigit != 0) {
ckDigit = 10 - ckDigit; }

return ckDigit;
}

//Calculates the check digit for a UPC-A number.
function UPC(strUPC)
{
var temp;
var ckDigit;
var number = new String();
var digits = new Array( );
var i = 0;

number = strUPC;

while (i <= number.length) { //This while statement seperates the string
temp = number.charAt(i); //into characters then turns the characters into
temp = parseInt(temp); //integers. The integers are then put into an array.
digits[i] = temp;
i++; }

//This next line computes a check digit. If modulo 10 produces a remainder then the remainder
// is subtracted from 10, to produce the check digit.
ckDigit = ( ( (digits[0]+digits[2]+digits[4]+digits[6]+digits[8]+digits[10]) * 3 ) + (digits[1]+digits[3]+digits[5]+digits[7]+digits[9] ) ) % 10;
if (ckDigit != 0) {
ckDigit = 10 - ckDigit; }

return ckDigit;
}

//Calculates the check digit for a Bill of Lading number.
function BOL(strBOL)
{
var temp;
var ckDigit;
var number = new String();
var digits = new Array( );
var i = 0;

number = strBOL;

while (i < number.length) { //This while statement seperates the string
temp = number.charAt(i); //into characters then turns the characters into
temp=parseInt(temp); //integers. The integers are then put into an array.
digits[i] = temp;
i++; }

alert(i);

ckDigit = ( (digits[0] + digits[2] + digits[4] + digits[6] + digits[8] + digits[10] + digits[12] + digits[14] ) + ( (digits[1] + digits[3] + digits[5] + digits[7] + digits[9] + digits[11] + digits[13] + digits[15] ) *3) ) % 10;
if (ckDigit != 0) {
ckDigit = 10 - ckDigit; }

return ckDigit;
}

[r-senior]

I'm going to bed, but have a go with this:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char **argv)
{
        int i, odd_sum = 0, even_sum = 0, sum, check_digit;
        char *base;

        if (argc != 2) {
                fprintf(stderr, "Error: Wrong number of arguments\n");
                exit(EXIT_FAILURE);
        }

        base = argv[1];

        if (strlen(base) != 7) {
                fprintf(stderr, "Error: Argument is not 7 characters\n");
                exit(EXIT_FAILURE);
        }

        for (i = 0; i < 7; i += 2) {
                // Odd digits
                odd_sum += base[i] - '0';
        }

        for (i = 1; i < 7; i += 2) {
                // Even digits
                even_sum += base[i] - '0';
        }

        sum = odd_sum * 3 + even_sum;
        check_digit = (10 - (sum % 10)) % 10;
        printf("%s%d\n", base, check_digit);

        return(EXIT_SUCCESS);
}

It's C, so you'll need gcc installed. Paste that into a file called ean8.c and compile it like this:

$ make ean8

Or if that doesn't work:

$ gcc -o ean8 ean8.c

I checked a few numbers against a web-based EAN-8 check digit thingy and it seemed OK, but I have just written it in five minutes. Once you have the ean8 executable, it needs to be in your path - I'd suggest ~/bin.

Then you can just do something like:

answer=$(ean8 $code)

EDIT: When I see that amount of code, I start to think I did something wrong. I think it's because I only deal with 7 digits.

[Eiji Takanaka]

cool i'll give it a scout,

thanks for the suggestions man!

[Eiji Takanaka]

Haha aye, that javascript is for a whole host of algorithms.

O.k i've got everything set, exectuables in /bin....

So now to integrate.....

I'll let ya know how my experiments unfold

[Eiji Takanaka]

#!/bin/bash

for i in {0..9999}; do
code=$(printf "%04d"000 $i)
ans=$(ean8 $code)
echo $(date +%H:%M:%S)
echo $(date +%H:%M:%S) >> /home/User/log.txt
echo 'wpa_cli wps_reg 00:00:00:00:00:00' $ans
echo 'wpa_cli wps_reg 00:00:00:00:00:00' $ans >> /home/User/log.txt
wpa_cli wps_reg 00:00:00:00:00:00 $ans
sleep 9

done

& output..

01:47:25
wpa_cli wps_reg 00:00:00:00:00:00 64010007
Selected interface 'wlan0'
OK

This seems to work for me, i'll confirm the ean-8 values with the online calculator, but it seems to of done the trick!

Fascinating, so i've now called 2 programs from within this simple bash-script. And achieved the desired results.

Thanks a lot dude!

=)