A snippet of code to detect the path to the current script. Works in bash and zsh.

README.md

This snippet detects various information about the shell script in which it is being executed. Copy and paste it into the top of your script.

Variables set are as follows:

• $__SHELL: bash or zsh
• $__SOURCED: true if the file was invoked using source filename or . filename, otherwise it will be blank.
• $__SCRIPT_PATH: the full absolute path to the script.
• $__SCRIPT_DIR: the full absolute path to the script's directory.
• $__SCRIPT_PATH_DEREFERENCED: the full absolute path to the script, dereferencing all symbolic links.
• $__SCRIPT_DIR_DEREFERENCED: the full absolute path to the script's directory, dereferencing all symbolic links.

detect.sh

function realpath () {
    echo "$1" | python -c "import os.path, sys; print(os.path.abspath(sys.stdin.read().strip()))"
}

function dirname () {
    echo "$1" | python -c "import os.path, sys; print(os.path.dirname(sys.stdin.read().strip()))"
}

function dereference () {
    local link
    link="$1"
    while [ -L "$link" ]; do
        link=$(echo "$link" | python -c "import os, sys; print(os.readlink(sys.stdin.read().strip()))")
    done
    echo $link
}

if [[ "${BASH_SOURCE[0]}" != "" ]]; then
    # Bash
    __SCRIPT_PATH="${BASH_SOURCE[0]}"
    __SHELL="bash"
    if [[ ${BASH_SOURCE[0]} != $0 ]]; then
        __SOURCED=true
    fi
elif [[ "$zsh_eval_context" != "" ]]; then
    # zsh
    __SCRIPT_PATH="$0"
    __SHELL="zsh"
    if [[ $zsh_eval_context =~ "file" ]]; then
        __SOURCED=true
    fi
fi

__SCRIPT_PATH=$(realpath "$__SCRIPT_PATH")
__SCRIPT_DIR=$(dirname "$__SCRIPT_PATH")

__SCRIPT_PATH_DEREFERENCED=$(dereference "$__SCRIPT_PATH")
__SCRIPT_DIR_DEREFERENCED=$(dereference "$__SCRIPT_DIR")

If you change those echo statements to printf %s "$1" then you can remove the calls to .strip() considering that they could erroneously remove legitimate whitespace.