Find installation folder for bash scripts

24 Apr 2021

This is the start of a series on some bash tricks and features that I’ve developed for the bashew bash scripting micro-framework.

A problem I have spent some time on during the development of bashew, is locating the exact folder where the executing script is running from.

# a script can be called in 3 different ways:
# 1) with an explicit full path
/usr/local/bin/gettext.sh # example
# getting the folder is easy
script_folder="$(dirname "$0")"

# 2) with a explicit relative path
../install/build.sh # example
# getting the folder is a bit more complex
script_folder="$(dirname "$0")"
script_folder="$(cd -P "$script_folder" && pwd)"

# 3) without an explicit path
setver.sh # example
# this means the script can be found in the path
script_path="$(which "$0")"
script_folder="$(dirname "$script_path")"

This does however not take into account symlinks (symbolic links), and those are often used for scripts installed with a package manager, like basher. My scripts typically have nested symlinks after installation by basher.

$HOME/.basher/cellar/bin/setver -> $HOME/.basher/cellar/packages/pforret/setver/setver -> $HOME/.basher/cellar/packages/pforret/setver/setver.sh

These nested symlinks have to be resolved until the real physical folder has been found, a task best done by a recursive readlink function.

This is how bashew does it:

recursive_readlink() {
    [[ ! -L "$1" ]] && echo "$1" && return 0

    local file_folder
    local link_folder
    local link_name
    local symlink
    
    file_folder="$(dirname "$1")"
    [[ "$file_folder" != /* ]] && 
      link_folder="$(cd -P "$file_folder" &>/dev/null && pwd)"
    symlink=$(readlink "$1")
    link_folder=$(dirname "$symlink")
    link_name=$(basename "$symlink")
    [[ -z "$link_folder" ]] && 
      link_folder="$file_folder"
    [[ "$link_folder" == \.* ]] && 
      link_folder="$(cd -P "$file_folder" && cd -P "$link_folder" &>/dev/null && pwd)"
    recursive_readlink "$link_folder/$link_name"
}

script_install_path="${BASH_SOURCE[0]}"
script_install_path=$(recursive_readlink "$script_install_path")
script_install_folder="$( cd -P "$( dirname "$script_install_path" )" && pwd )"

Peter Forret

Find installation folder for bash scripts

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