Shell Script: Arithmetic operation in array - bash

Question

I'm doing for fun and this as part of my learning process in Shell scripting.
Let say I have initial input A B C
What I'm trying to do is to split the string and convert each of them to decimal value.
A B C = 65 66 67
Then I'll add the decimal value to random number, let say number 1.
Now, decimal value will become = 66 67 68
Finally, I'll convert the decimal to the original value again which will become B C D
ubuntu#Ubuntu:~$ cat testscript.sh -n
#!/bin/bash
1 string="ABC"
2
3 echo -e "\nSTRING = $string"
4 echo LENGTH = ${#string}
5
6 # TUKAR STRING KE ARRAY ... word[x]
7 for i in $(seq 0 ${#string})
8 do word[$i]=${string:$i:1}
9 done
10
11 echo -e "\nZero element of array is [ ${word[0]} ]"
12 echo -e "Entire array is [ ${word[#]}] \n"
13
14 # CHAR to DECIMAL
15 for i in $(seq 0 ${#string})
16 do
17 echo -n ${word[$i]}
18 echo -n ${word[$i]} | od -An -tuC
19 chardec[$i]=$(echo -n ${word[$i]} | od -An -tuC)
20 done
21
22 echo -e "\nNEXT, DECIMAL VALUE PLUS ONE"
23 for i in $(seq 0 ${#string})
24 do
25 echo `expr ${chardec[$i]} + 1`
26 done
27
28 echo
This is the output
ubuntu#Ubuntu:~$ ./testscript.sh
STRING = ABC
LENGTH = 3
Zero element of array is [ A ]
Entire array is [ A B C ]
A 65
B 66
C 67
NEXT, DECIMAL VALUE PLUS ONE
66
67
68
1
As you can see in the output, there are 2 problems (or maybe more)
The last for loop processing additional number. Any idea how to fix this?
NEXT, DECIMAL VALUE PLUS ONE
66
67
68
1
This is the formula to convert decimal value to char. I'm trying to put the last value to another array and then put it in another loop for this purpose. However, I'm still have no idea how to do this in loop based on previous data.
ubuntu#Ubuntu:~$ printf "\x$(printf %x 65)\n"
A
Please advise

Answer 1

Using bash you can replace all of your code with this code:
for i; do
printf "\x"$(($(printf '%x' "'$i'") +1))" "
done
echo
When you run it as:
./testscript.sh P Q R S
It will print:
Q R S T

Answer 2

awk to the rescue!
simpler to do the same in awk environment.
$ echo "A B C" |
awk 'BEGIN{for(i=33;i<127;i++) o[sprintf("%c",i)]=i}
{for(i=1;i<=NF;i++) printf "%c%s", o[$i]+1, ((i==NF)?ORS:OFS)}'
B C D

Answer 3

seq is from FIRST to LAST, so if your string length is 3, then seq 0 3 will give you <0,1,2,3>. Your second to last loop (lines 16-20) is actually running four iterations, but the last iteration prints nothing.
To printf the ascii code, insert it inline, like
printf "\x$(printf %x `expr ${chardec[$i]} + 1`) "
or more readably:
dec=`expr ${chardec[$i]} + 1`
printf "\x$(printf %x $dec)\n"