find-bin-dir.sh

#!/usr/bin/env bash

# Find possible writable binary directory

set -o pipefail
set -o errexit
set -o nounset
#set -o xtrace

# Set magic variables for current file & dir
__dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
__file="${__dir}/$(basename "${BASH_SOURCE[0]}")"
readonly __dir __file

init_user_home_bin() {
  if [ ! -d "$(cd; pwd)/bin" ]; then
    mkdir -p "$(cd; pwd)/bin"
  fi
}


writable_bin_path() {
  local path_delimiter IFS paths
  path_delimiter=$(echo ${PATH} | grep -oE '[;:]' | head -1)
  while IFS="${path_delimiter}" read -ra paths; do
    for i in "${paths[@]}"; do
      if echo "${i}" | grep -E '^(/usr/|'$(cd; pwd)')' | grep -vE '(composer|vendor)' > /dev/null && [[ "${i}" =~ \/bin$ ]]; then
        if touch ${i}/test_touch 2> /dev/null; then
          rm -rf ${i}/test_touch
          echo ${i}
          break
        fi
      fi
    done
  done <<< "$PATH"
}

init_user_home_bin

writable_bin_path

Test with and without SUDO:

$ sudo bash find-bin-dir.sh
/usr/bin

$ bash find-bin-dir.sh
/home/myuser/bin