Pass arguments to shell function by reference

Question

I have a function to which Iam trying to send the array elements-

for (( idx=5 ; idx < ${#arr[*]} ; idx++ )); do
            escape_html ${arr[idx]} 
    done
function escape_html() {
x=$1
out="${x/>/%gt;}"
out="${x/</%lt;}"
}

I want the value of the array element to be changed if they have > or < after the function call (just as we use in call by reference). In this code, Iam passing the value to another variable. Idont want to do that. I want to do such operations directly on my argument and want those changes to be reflected the next time I try to access those array elements

Assign the result of the `escape_html` function to the array index in the loop. — Etan Reisner, Apr 06 '15 at 16:28
@EtanReisner Actually we are dealing with a string here(argument). So I cant return it since the function can return only integers — , Apr 06 '15 at 16:48
You can absolutely capture the output of a function which, in this case, is the "result" and the desired value. — Etan Reisner, Apr 06 '15 at 16:56

score 2 · Answer 1 · edited May 23 '17 at 12:06

If you want to do this correctly, have the loop update its own reference with array[idx]=$(yourfunction "${array[idx]}").

If you really want to do it the way you propose anyways, which is bad practice and has some caveats related to special variables and scope, pass the name and index rather than the value, then assign and reference indirectly:

#!/bin/bash
modify_arguments() {
  local var=$1
  local value=${!var}
  printf -v "$var" "${value//foo/bar}"
}

array=(food foodie fool fooled)

echo "Before: $(declare -p array)"
for i in {2..3}
do
  modify_arguments "array[i]"
done
echo "After:  $(declare -p array)"

Outputs:

Before: declare -a array='([0]="food" [1]="foodie" [2]="fool" [3]="fooled")'
After:  declare -a array='([0]="food" [1]="foodie" [2]="barl" [3]="barled")'

score 1 · Answer 2 · answered Apr 06 '15 at 16:46

1

Variable idx and array arr are globals, no need to pass to function.

#!/bin/bash

function escape_html() {
  arr[idx]="${arr[idx]/>/%gt;}"
  arr[idx]="${arr[idx]/</%lt;}"
}

arr=(foo foo foo foo foo "<html>" "<xml>" "<bar>")

for (( idx=5 ; idx < ${#arr[*]} ; idx++ )); do
  echo ${arr[idx]}         # before function call
  escape_html
  echo ${arr[idx]}         # after funtion call
done

answered Apr 06 '15 at 16:46

Cyrus

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If I give a printf " ${arr[5]} \n" after that for loop, Iam getting an error : printf: `;': invalid format character . Do you have any idea why that is happening? – Apr 06 '15 at 17:09
Use `printf "%s\n" " ${arr[5]}"`. – Cyrus Apr 06 '15 at 17:12

Pass arguments to shell function by reference

2 Answers2