suggested_install.sh

#!/bin/env bash

print_usage() {
    self_filename="${0##*/}"
    echo "usage: \"${self_filename}\" [-h] [DIR...]"
    echo \
'
Search set of folders until one is found in the systems $PATH with write
access. Use it to install the files as commands into the folder. Without DIR
arguments a list of default folders are searched.

positional arguments:
  DIR                  folders to look for when searching for installation path

options:
  -h                   print this help and exit'
}

# Default path to search with priority, if no arguments are given.
default_install_dir=""
install_cmd="$(/usr/bin/which install)"

while getopts ':h' OPTION
do
    case "$OPTION" in
        h) print_usage
            exit 0
            ;;
        ?) continue ;;
    esac
done

# This variable will be set by the following function if any usable path is
# found. Then later functions will use it as base folder to install into.
install_dir=""
# This one will also be set by the following function. Can be useful to print
# in case of a problem.
list_of_install_dirs=""

# Searches the list of system $PATH if any of the given directories are found
# in it. If so, then update the variable "install_dir" with it, when user has
# write permission. If no arguments to the function are given, then it defaults
# to some predefined set of directories to look for.
find_install_dir () {
    if [ ${#} -eq 0 ]
    then
        list_of_install_dirs=(
            "${default_install_dir}"
            "$(systemd-path user-binaries)"
            "$HOME/.local/bin"
            "$HOME/bin"
            "/usr/local/bin"
            )
    else
        list_of_install_dirs=("${@}")
    fi

    # Convert the system $PATH variable into a Bash list.
    IFS=: read -r -d '' -a list_of_path < <(printf '%s:\0' "$PATH")

    for dir in "${list_of_install_dirs[@]}"
    do
        for path in "${list_of_path[@]}"
        do
            if [ "${path}" == "${dir}" ]
            then
                if [ -w "${path}" ]
                then
                    install_dir="${path}"
                else
                    echo "No write permission for install directory:"
                    echo "        ${path}"
                    exit 1
                fi
                return
            fi
        done
    done
}

# Install the given "filename" as a command into the previously set
# "install_dir". It will remove the file extension, so it works like any
# normal system command. Second argument can be an option with special
# actions, such as creating an additional symbolic link.
install_program () {
    filename="${1}"
    file_no_ext="${filename%.*}"
    option="${2}"

    "${install_cmd}" -m 755 -b -C -D -t "${install_dir}" "${filename}"

    if ! [ "${?}" == 0 ]
    then
        exit 1
    else
        mv -f "${install_dir}/${filename}" "${install_dir}/${file_no_ext}"

        if [ "${option}" == "--symlink" ]
        then
            ln --symbolic \
                "${install_dir}/${file_no_ext}" \
                "${install_dir}/${filename}"
        fi
    fi

    if [ -f "${install_dir}/${file_no_ext}" ]
    then
        echo ""
        echo "${filename} installed as:"
        echo "        ${install_dir}/${file_no_ext}"
        if [ "${option}" == "--symlink" ]
        then
            echo "        ${install_dir}/${filename}"
        fi
    else
        echo "Error! Could not install ${filename} to ${install_dir}"
        exit 1
    fi
}

# Simple question to answer with "y" for proceeding. Any other key than "y"
# will cause to end the script.
ask_proceed () {
    echo "Continue installallation programs to:"
    echo "        ${install_dir}"
    echo ""
    echo "(Y)es or (N)o:"

    read -rt 10 answer

    first_letter="${answer:0:1}"
    if ! [[ "${first_letter}" == "y" || "${first_letter}" == "Y" ]]
    then
        exit 1
    fi
}

if [ $# -eq 0 ]
then
    find_install_dir
else
    find_install_dir "${@}"
fi

if [ "${install_dir}" == "" ]
then
    echo "Error! No usable install directory could be recognized from:"
    echo "     \"${list_of_install_dirs[*]}\" "
    exit 1
else
    ask_proceed
fi

# Find install dir and install following files by removing their extension.
install_program "fp"