1

This is my code to write a function which prints the Fibonacci numbers 

function fib {
        fib_array=( 0 1 )
        count=3

        while [[ $count -le $1 ]]
        do
                fib_new=$(( ${fib_array[-1]} + ${fib_array[-2]} ))
                fib_array+=( $fib_new )
                let count=$count+1
        done

        echo " ${fib_array[*]}"
}

When I run my bash with fib 5, I keep getting the messages :

-bash: fib_array: bad array subscript
-bash: fib_array: bad array subscript
-bash: +  : syntax error: operand expected (error token is " ")

I assume the there might be some problems in the 1st line within the while do, i.e. fib_new=$(( ${fib_array[-1]} + ${fib_array[-2]} )) but don't know how to modify.

Can anyone help?

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2
  • I could not reproduce it, I get the expected output: 0 1 1 2 3. Commented Apr 18, 2020 at 22:00
  • 1
    What is your version of bash? negative array subscripts were introduced in 4.3 if I'm reading the NEWS file correctly Commented Apr 18, 2020 at 22:11

2 Answers 2

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1

It seems that you are using a version of bash that doesn't understand a negative array like array[-1]. You could install a more recent version of bash (above 4.3) or you can try this script:

fib () {
          fib_array=( 0 1 ); size=2
          limit=$1

          while [[ size -lt limit ]]
          do
              fib_arr+=( "$(( ${fib_arr[size-1]} + ${fib_arr[size-2]} ))" )
              size=${#fib_arr[@]}
          done

          echo " ${fib_arr[*]}"
}

fib "${1:-10}"

which use the size (of the array) variable to avoid negative indexes.

Or, if you want a slightly faster option that works for all bash shells, use:

fib () {
         limit=$1
         set -- 0 1
         printf '%s %s' "$1" "$2"; count=3
         while [ "$count" -le "$limit" ]; do
              t33=$(($1+$2))
              set -- "$2" "$t33"
              printf ' %s' "$t33"
              count=$((count+1))
         done
         echo
       }

fib ${1:-10}
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-1

You need to put [count-1] instead if [-1] and [count-2] instead if [-2]

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1
  • This has already been covered in another answer. Commented Apr 19, 2020 at 7:05

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