Bash - array as argument

Question

I have a problem with using array as parameter in function.

#!/usr/bin/env bash

function array_param
{
  local ARRAY_s; local ARRAY_t; local OPTIND

  while getopts 's:t:' opt ; do
    case "$opt" in
      s) ARRAY_s=$OPTARG;;
      t) ARRAY_t=$OPTARG;;      
    esac
  done
  shift $((OPTIND-1))
  echo "ARRAY_s=${ARRAY_s[@]}; ARRAY_t=${ARRAY_t[@]}"
}

array_s=(100 200 300)
array_t=(0 10 3585)

array_param -s ${array_s} -t ${array_t}

Why is only the first element assigned to variables ARRAY_s and ARRAY_t?

Result: ARRAY_s=100; ARRAY_t=0

${array_s} is the first element of the array. Try "${array_s[@]}" — 123
– 123, Commented Jan 12, 2018 at 13:29
ARRAY_s=$OPTARG is also only a string assignment, not an array assignment. What are you trying to do exactly? Copy arrays following the parameters to ARRAY_s and ARRAY_t? — PesaThe
– PesaThe, Commented Jan 12, 2018 at 13:31
Yes, I try to assign the -s and -t parameters to a variable and use it in a function (I only inserted a fragment that I can't solve). — skolukmar
– skolukmar, Commented Jan 12, 2018 at 13:40

Nahuel Fouilleul · Accepted Answer · 2018-01-12 14:56:10Z

1

modifying slightly function (using lowercase for variable, and using array semantics)

array_param() {
    local l_array_s l_array_t OPTIND

    while getopts 's:t:' opt ; do
        case "$opt" in
        s) l_array_s+=( "$OPTARG" ) ;;
        t) l_array_t+=( "$OPTARG" ) ;;
        esac
    done
    shift $((OPTIND-1))
    echo "l_array_s=${l_array_s[*]}; l_array_t=${l_array_t[*]}"
}

can be called

array_param "${array_s[@]/#/-s}" "${array_t[@]/#/-t}"

${array_s[@]/#/-s} notation is specificc to bash, # matches start of string and is replaced by -s for each element in array.

following printf to understand how arguments are passed

printf "<%s> " "${array_s[@]/#/-s}" "${array_t[@]/#/-t}"

also compare

printf "<%s> " "${array_s}"
printf "<%s> " "${array_s[@]}"
printf "<%s> " "${array_s[*]}"

edited Jan 12, 2018 at 14:56

answered Jan 12, 2018 at 14:37

Nahuel Fouilleul

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2 Comments

PesaThe Over a year ago

You are missing quotes "$OPTARG". Otherwise, interesting use of /#/-s...+1.

Nahuel Fouilleul Over a year ago

@PesaThe, true, fixed

PesaThe · Accepted Answer · 2018-01-12 15:01:59Z

${array_s} is equivalent to ${array_s[0]}, that's why only the first element is assigned:

#!/usr/bin/env bash

array_param() {   
    local opt OPTIND tmp
    local -a arr_s arr_t

    while getopts 's:t:' opt; do
        case $opt in
            s) tmp=$OPTARG[@]; arr_s=("${!tmp}") ;;
            t) tmp=$OPTARG[@]; arr_t=("${!tmp}") ;;
        esac
    done
    echo "arr_s = ${arr_s[*]}"
    echo "arr_t = ${arr_t[*]}"
}

arr1=(100 200 300)
arr2=(0 10 3585)

array_param -s arr1 -t arr2

local opt: you should localize all variables, even opt
tmp=$OPTARG[@]: creates a tepmporary variable of this format: array_name[@]
arr=(values): array assignment
${!tmp}: variable indirection. It first expands to the value of $tmp, and then expands once more to the final result: ${!tmp} -> ${array_name[@]} -> all values

You can also use nameref (makes the code more readable but requires bash 4.3 or later):

s) local -n tmp=$OPTARG; arr_s=("${tmp[@]}") ;;
t) local -n tmp=$OPTARG; arr_t=("${tmp[@]}") ;;

sahaquiel · Accepted Answer · 2018-01-12 13:47:17Z

You can't pass array_s and array_t as array, getopts will get only first element of each array.

But, you can try to use C-style for loop like that to increment local ARRAY_s and ARRAY_t variable, print them in the end:

    $ cat optarg.sh 
    #!/usr/bin/env bash

    function array_param
    {
      local OPTIND

      while getopts 's:t:' opt ; do
        case "$opt" in
            s) ARRAY_s+=("${OPTARG}");;
            t) ARRAY_t+=("${OPTARG}");;      
        esac
      done
      shift $((OPTIND-1))
    }

    array_s=(100 200 300)
    array_t=(0 10 3585)

    #Works if only array_s length equal array_t length.
    for ((args=0; args<${#array_s[@]}; args++))
    do
        array_param -s ${array_s[args]} -t ${array_t[args]}
    done

    echo "ARRAY_s=${ARRAY_s[@]}; ARRAY_t=${ARRAY_t[@]}"

Output:

ARRAY_s=100 200 300; ARRAY_t=0 10 3585

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