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I created dynamic variables.

for (( c=1; c<=2; c++ ))
do  
   eval "prev$c=$number";
done

prev1, prev2

for (( c=1; c<=2; c++ ))
do  
   eval "current$c=$number";
done

current1, current2

if I have the variables

$prev1 is 1
$prev2 is 2
$current1 is 1
$current2 is 3

How do I compare inside a loop with if? Below is wrong, could someone correct the syntax? Thanks in advance.

for (( c=1; c<=2; c++ ))
do  
 if ((prev$i != current$i)); then
    echo "prev$i is $prev[i] and current$i is $current[i], they are different"
  fi
done
Improve this question
2
  • 1
    Use arrays instead. Commented Jul 9, 2021 at 7:39
  • You seem to partially be using array syntax already. You could just use arrays. If you describe what it is you're actually doing (what prev and current are), then we might be able to help you with an even better solution. Commented Jul 9, 2021 at 8:13

1 Answer 1

Reset to default
3

In bash, you can use variable indirection

    prev=prev$c
    current=current$c

    if ((${!prev} != ${!current})); then
        echo "prev$c is ${!prev} and current$c is ${!current}, they are different"
    fi

But using arrays is safer (no eval):

#! /bin/bash
number=0
for (( c=1; c<=2; c++ )) ; do
    prev[c]=$number
    number=$c
    current[c]=$number

    if ((${prev[c]} != ${current[c]})); then
        echo "prev$c is ${prev[c]} and current$c is ${current[c]}, they are different"
    fi
done
Improve this answer
2
  • 1
    I have a feeling that if we were to be shown more of the user's code, it may well be enough with a single prev and a single current variable, possibly by swapping a couple of loops around. Commented Jul 9, 2021 at 9:19
  • 1
    @Kusalananda: Yes, I rarely use more than one $previous. Commented Jul 9, 2021 at 9:20

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