How I can delete element from original array by indirect reference to it

Question

I have three arrays:

array1=(8 7 6 5 4 3 2 1)
declare -a array2
declare -a array3

And X that representing which array I should use for some operation So, first of all I am finding it like this:

nameOfArray=array$X[@]
indirectTempArray=("${!nameOfArray}")
echo ${indirectTempArray[@]}  // returns 8 7 6 5 4 3 2 1 in case if X == 1

So, the question is, how I can delete value from original array which reference I have?

Do you want to keep the original indices? – kvantour Dec 20 '19 at 18:10 — kvantour, Dec 20 '19 at 18:10

score 2 · Answer 1 · answered Dec 20 '19 at 18:20

2

You can pass a plain string to unset:

array1=(8 7 6 5 4 3 2 1)
X=1
unset "array$X[1]"
declare -p array1

results in the array without the second element (index 1):

declare -a array1=([0]="8" [2]="6" [3]="5" [4]="4" [5]="3" [6]="2" [7]="1")

answered Dec 20 '19 at 18:20

that other guy

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This is exactly what I needed. Thank you!) By the way, how I can add value to array$X? – Булат Хайруллин Dec 20 '19 at 22:11
@БулатХайруллин `declare "array$X[42]=1337"` – that other guy Dec 20 '19 at 22:16
When I do it like this: eval array$X+=${array[-1]} array$X will have 1 eval array$X+=${array[-2]} array$X will have 12 instead of 1 2 eval array$X+=${array[-3]} array$X will have 123 instead of 1 2 3 – Булат Хайруллин Dec 20 '19 at 22:17
I need to add value to the end of array$X – Булат Хайруллин Dec 20 '19 at 22:22
1

`declare "array$X+=(42)"` – that other guy Dec 20 '19 at 22:25

kvantour · Answer 2 · 2019-12-20T18:54:24.360

If you really want to do it, I would combine the following two ideas:

BashFAQ/06 Evaluating Indirect references

$ realarray=(...); ref=realarray; index=2
$ tmp=${ref}[index]
$ echo "${!tmp}"

Remove an element from a Bash array

delete by key:

$ realarray=( 5 4 3 2 1 "foo bar" ); ref=realarray; key=2
$ tmp=${ref}[@]; tmp=( "${!tmp}" )
$ unset "$ref"'['"$key"']'
$ echo "${realarray[@]}"
5 3 2 1 foo bar
$ echo "${#realarray[@]}"
5

delete by value:

$ realarray=( 5 4 3 2 1 "foo bar" ); ref=realarray; value=2
$ tmp=${ref}[@]; tmp=( "${!tmp}" )
$ eval "$ref=()"
$ for i in "${tmp[@]}"; do [ "$i" != "$value" ] && eval "$ref+=(\"$i\")"; done
$ echo "${realarray[@]}"
5 4 3 1 foo bar
$ echo "${#realarray[@]}"
5

This removes the element from the array and solves quoting issues. You could write this a bit different by using a second temporary and a single eval, but the idea is the same.

How I can delete element from original array by indirect reference to it

2 Answers2