awk: counting fields in a variable - awk

Question

Given a string like {running_db_nodes,[ejabberd#host002,ejabberd#host001]}, , how could the number of comma-delimited strings in square brackets be counted?
The useful substring can be extracted with gensub:
awk '/running_db_nodes/ {print gensub(/ {running_db_nodes,\[(.*)\]},/, "\\1", 1)}' .
A naive approach with NF gets fields from the original input string:
awk -F, '/running_db_nodes/ {nodes=gensub(/ {running_db_nodes,\[(.*)\]},/, "\\1", 1); print NF}'
How could the number of fields in a variable like nodes in the last example be extracted?

Answer 1

You can set your FS to characters [ and ], then split your $2 to an array and capture the count of elements returned from split():
echo "{running_db_nodes,[ejabberd#host002,ejabberd#host001]}," |
awk -F"[][]" '{print split($2,a,",")}'
2

Answer 2

With your shown samples only and with shown attempts please try following awk code.
echo "{running_db_nodes,[ejabberd#host002,ejabberd#host001]}," |
awk '
{
gsub(/.*\[|\].*$/,"")
print gsub(/,/,"&")+1
}
'
Explanation: Simple explanation would be:
gsub(/.*\[|\].*$/,""): Globally substituting everything from starting to till [ AND substituting from [ to till end of value with NULL in current line.
print gsub(/,/,"&")+1: Globally substituting , with itself(just to count it) and adding 1 to it and printing it as pre requirement.

Answer 3

A naive approach with NF gets fields from the original input string
gensub does not change string it is working on, you might use sub (or gsub) which will alter string it is working at which will alter relevant built-in variables values that is
echo "{running_db_nodes,[ejabberd#host002,ejabberd#host001]}" | awk 'BEGIN{FS=","}{sub(/^.*\[/,"");sub(/].*$/,"");print NF}'
gives output
2
Explanation: use sub to delete everything before [ and [, then ] and everything behind it, print number of fields.
(tested in GNU Awk 5.0.1)