how do i loop through an array of numbers and update the array in bash using the array values-CodePudding

I am trying to increase the values of an array of integers using a variable, but it doesn't seem to be accessing the array values properly. It is to start from 0 in an ascending order, while incrementing the current array value at each iteration. I tried this:

array=(2 0 1)
tag=(H H H)
count=0

for i in ${array[@]}
do
    if [[ "$array[$i]"="$count" ]]
    then
        array[$i]=$((${array[$i]} 1)) 
        tag[$i]="C"
    fi
count=$(($count   1))
done

Instead it kept updating from 2, then 1, before 0. I want it to start from 0, since that is the index that is equal to count. This was the output.

 0       H H C
         2 0 2

 1       C H C
         3 0 2

 2       C C C
         3 1 2

CodePudding user response：

One problem is that the values you are retrieving with the for loop are integers that are being used as indexes to update the values of the array. A second problem is that your conditional statement is actually an assignment, so its exit code is always 0 (true), so $count, though incrementing, affects nothing.

First time through, $i==2, the third element of array is incremented (array[2]==2), the third element of the tag array is set to changed

The second time through, $i==0, the first element of array is incremented (array[0]==3), the first element of tag array is set to changed.

The third time through, $i==1 (see comment below), the second element of array is incremented (array[1]==1), and the second element of the tag array is set to changed.

Promised comment: In the third iteration, other languages would have $i==2 because array[2] had been incremented in the first loop. Bash is apparently iterating over the original values of the array, despite subsequent changes.

I think what you want to do is:

declare -a array=(2 0 1)
declare -a tag=("here" "here" "here")
declare -i count=0
declare -i i

echo "$count:  ${array[*]}"
echo "   ${tag[*]}"

for (( i=0; i<${#array[*]};   i )); do
    (( array[i]   ))   # no need for '$' within (( ))
    tag[$i]="changed"
    (( count   ))
    echo "$count:  ${array[*]}"
    echo "   ${tag[*]}"
done

I didn't include your conditional because I can't figure out what you're trying to do with it.

I added the echo statements to create output similar to the output you claimed in your example.

CodePudding user response：

In the loop iteration you are using array values instead of array indices, which is the core of the problem. So the TL;DR is: "${!array[@]}".

array=(2 0 1)
tag=(H H H)
echo "${array[@]@A}; ${tag[@]@A};"

for index in "${!array[@]}"; do
  ((  array[index]))
  tag[index]=C
  echo "${array[@]@A}; ${tag[@]@A};"
done

Output:

declare -a array=([0]="2" [1]="0" [2]="1"); declare -a tag=([0]="H" [1]="H" [2]="H");
declare -a array=([0]="3" [1]="0" [2]="1"); declare -a tag=([0]="C" [1]="H" [2]="H");
declare -a array=([0]="3" [1]="1" [2]="1"); declare -a tag=([0]="C" [1]="C" [2]="H");
declare -a array=([0]="3" [1]="1" [2]="2"); declare -a tag=([0]="C" [1]="C" [2]="C");

CodePudding user response：

FYI: Bash indexing starts from 0 (so to change the 2-nd element you should consider index No. 1) script.sh

#!/bin/bash

array=(2 0 1)
tag=(H H H)

for i in `seq 1 ${#array[@]}` ;do
  (( i-- ))
  ii="${array[i]}"
  (( ii-- ))
  tag[$ii]="C"
  #(( array[i]   ))
  echo -e "$i:\t${tag[@]} \n\t${array[@]}"
done

Output of the script.sh:

Update:

Just seen your comment, will try to update my script.

I want it to start from the array value 0, which is is the middle. So it should look like this, H C H > H C C > C C C

Script Updated, please check again!