Dynamic indirect Bash array

Question

I have logs in this format:

log1,john,time,etc
log2,peter,time,etc
log3,jack,time,etc
log4,peter,time,etc

I want to create a list for every per

Answer 1

Be warned: The below uses namevars, a new bash 4.3 feature.

---

First: I would strongly suggest namespacing your arrays with a prefix to avoid collisions with unrelated variables. Thus, using content_ as that prefix:

read_arrays() {
  while IFS= read -r line && IFS=, read -r -a fields <<<"$line"; do
    name=${fields[1]}
    declare -g -a "content_${fields[1]}"
    declare -n cur_array="content_${fields[1]}"
    cur_array+=( "$line" )
    unset -n cur_array
  done
}

Then:

lines_for() {
  declare -n cur_array="content_$1"
  printf '%s\n' "${#cur_array[@]}" ## emit length of array for given person
}

...or...

for_each_line() {
  declare -n cur_array="content_$1"; shift
  for line in "${cur_array[@]}"; do
    "$@" "$line"
  done
}

Tying all this together:

$ read_arrays <<'EOF'
log1,john,time,etc
log2,peter,time,etc
log3,jack,time,etc
log4,peter,time,etc
EOF
$ lines_for peter
2
$ for_each_line peter echo
log2,peter,time,etc
log4,peter,time,etc

---

...and, if you really want the format you asked for, with the number of columns as explicit data, and variable names that aren't safely namespaced, it's easy to convert from one to the other:

# this should probably be run in a subshell to avoid namespace pollution
# thus, (generate_stupid_format) >output
generate_stupid_format() {
  for scoped_varname in "${!content_@}"; do
    unscoped_varname="${scoped_varname#content_}"
    declare -n unscoped_var=$unscoped_varname
    declare -n scoped_var=$scoped_varname
    unscoped_var=( "${#scoped_var[@]}" "${scoped_var[@]}" )
    declare -p "$unscoped_varname"
  done
}