bash - How to allocate array which is passed to a function by name -

i want create function iterates through array , inserts given value, if not yet included. using function on 2 different parts of code , have use different arrays. therefore delivering array names function. can't figure out how allocate slot of array store element @ place.

here code:

name=("hello" "world")  function f {     array_name=$2[@]     array=("${!array_name}")     length=${#array_name[@]}     (( = 0; <= $length; i++ ));         if [[ "${array[i]}" = "$1" ]];             break;         fi         if [[ "$i" = "$length" ]];             ${2[$length+1]=$1};         fi     done }  f "test" "name" 

edit: want array append given value this

for in ${name[@]}     echo $i done 

would have output:

hello world test 

but apparently "${2[$length+1]=$1}" not working.

(idea passing array here: bash how pass array argument function)

if understand correctly want append value array if value not yet in array, tricky part array name passed function.

method 1

one possibility see problem different viewpoint: can pass function value inserted , full array, , function set global variable recover after execution. our test example we'll use:

array=( hello world "how today?" ) 

and we'll try insert test , hello (so hello not inserted):

f() { # function set global variable _f_out array obtained # positional parameters starting position 2, $1 appended if , # if $1 doesn't appear in subsequent positional parameters     local v=$1     shift     _f_out=( "$@" )     i; [[ $i = $v ]] && return; done     _f_out+=( "$v" ) } 

let's use it:

$ array=( hello world "how today?" ) $ f test "${array[@]}" $ array=( "${_f_out[@]}" ) $ printf '%s\n' "${array[@]}" hello world how today? test $ f hello "${array[@]}" $ array=( "${_f_out[@]}" ) $ printf '%s\n' "${array[@]}" hello world how today? test 

it works.

remark. used for i; do. it's nice shortcut for in "$@"; do.

method 2

you want fiddle simili-pointers , appending in place (this not in spirit of bash—that's why it's bit clumsy). tool use printf -v option: help printf:

-v var    assign output shell variable var rather           display on standard output 

the thing works array fields.

warning: might see other methods use eval. avoid them plague!

f() {     local array_name=$2[@]     local array=( "${!array_name}" )     in "${array[@]}"; [[ $i = $1 ]] && return; done     # $1 not found in array, let's append     printf -v "$2[${#array[@]}]" '%s' "$1" } 

and let's try it:

$ array=( hello world "how today?" ) $ f test array $ printf '%s\n' "${array[@]}" hello world how today? test $ f hello array $ printf '%s\n' "${array[@]}" hello world how today? test 

it works too.

note. both methods can have return code of function, e.g., 0 (success) if value inserted, , 1 (failure) if value there (or other way round)—the adaptation straightforward , left exercise. might useful in method 1 determine whether need update array returned value _f_out or not. in case, modify f doesn't set _f_out when value in array.

caveat. in both methods shown assumed arrays have contiguous indices start @ 0 (i.e., non-sparse arrays). think it's safe assumption here; if not case, these methods broken: first 1 (after reassignment) transform array non-sparse one, , second 1 might overwrite fields (as, array a, ${#a[@]} expands number of elements in array, not highest index + 1 found in array).