list handling in bash scripts

Question

I would like to do something that is very simple (and with a lot of tutorials) in other languages like python or C, but in bash script.

I would like to work with lists (of strings but could be for anything I suppose) In concrete I want to

Create an empty list
Add an element to the list
Check if the list is empty
Erase an element of the list
Refer to an element of the list by index (to go to "the next")

How can I implement this in bash script? (If lists are not available, perhaps then arrays?)

Bash just has arrays, which can be either indexed or associative. They can just contain strings, there are no higher level structures in bash. — Barmar, Aug 29 '21 at 06:34
Read about them in the [bash manual](http://www.gnu.org/software/bash/manual/html_node/Arrays.html#Arrays) — Barmar, Aug 29 '21 at 06:35
I have managed to resolve almost all of what I asked. The only thing I still don't know is how to remove an element of the array — KansaiRobot, Aug 29 '21 at 07:13
https://stackoverflow.com/questions/16860877/remove-an-element-from-a-bash-array — Barmar, Aug 29 '21 at 07:17
You could use a **Redis** list then your array would be accessible across your entire network, e.g. `redis-cli lpush array value` stores a value in a list and `redis-cli lset array 3 "hello"` changes entry 3 to "hello". — Mark Setchell, Aug 29 '21 at 08:11

KansaiRobot · Answer 1 · 2021-08-29T07:49:14.603

Before my question is closed ... I put here some answers

-Create an empty list

arr=()

-Add an element to the list

~~Not sure about this. I thought it was arr=($newvalue "$arr[@]") but it is not.~~

arr=( $newvalue "${arr[@]}")

Check if the list is empty

if ((${#arr[@]})); then   #the number is not 0
  echo "array is not empty"
else
  echo  "array is empty"
fi

Erase an element of the list OPEN QUESTION
Refer to an element of the list by index (to go to "the next")

echo ${arr[0]}

I think it is very important to put all these in a question and not going all around the internet to find the answers so here it goes

#create an empty array
arr=()
#arr=("eee")
echo "empty array"
echo ${arr[@]}
newvalue=000

#add new element
echo "add elements"

arr=("new_element" "${arr[@]}")
echo ${arr[@]}

arr=( $newvalue "${arr[@]}")
echo ${arr[@]}

echo "first element and number of elements"
echo ${arr[0]}   #refer to an element by index 
echo ${#arr[@]}  #number

echo "is it empty"
if ((${#arr[@]})); then   #the number is not 0
  echo "array is not empty"
else
  echo  "array is empty"
fi

echo "delete element"
arr=("${arr[@]/$newvalue}" )
echo ${arr[@]}

Add element to end of array with `arr+=("new element")` – Mark Setchell Aug 29 '21 at 08:04 — Mark Setchell, Aug 29 '21 at 08:04

list handling in bash scripts

1 Answers1