sh-realpath

• sh-realpath
  • Overview
  • Other Solutions
    • Install GNU Utils via Homebrew
      • Pearl
  • Usage
  • API
    • readlink Emulation
  • Quickstart

Overview

A portable, pure shell implementation of realpath

Copy the functions in realpath.sh into your shell script to avoid introducing a dependency on either realpath or readlink -f, since:

• realpath does not come installed by default
• readlink -f is not portable to OS-X

Other Solutions

Install GNU Utils via Homebrew

$ brew install coreutils

$ greadlink -f $FILE

export PATH="/usr/local/opt/coreutils/libexec/gnubin:$PATH"

Pearl

perl -MCwd -e 'print Cwd::abs_path shift' ~/non-absolute/file

Usage

$ source ./realpath.sh
$ realpath /proc/self
/proc/2772

Or we can get tricky:

    $ cd /tmp
    $ mkdir -p somedir/targetdir somedir/anotherdir
    $ ln -s somedir somedirlink
    $ ln -s somedir/anotherdir/../anotherlink somelink
    $ ln -s targetdir/targetpath somedir/anotherlink
    $ realpath .///somedirlink/././anotherdir/../../somelink
    /tmp/somedir/targetdir/targetpath

API

Note: unlike realpath(1), these functions take no options; do not use -- to escape any arguments

Function	Description
realpath PATH	Resolve all symlinks to PATH, then output the canonicalized result
resolve_symlinks PATH	If PATH is a symlink, follow it as many times as possible; output the path of the first non-symlink found
canonicalize_path PATH	Output absolute path that PATH refers to, resolving any relative directories (., ..) in PATH and any symlinks in PATH's ancestor directories

readlink Emulation

realpath.sh includes optional readlink emulation. It exposes a readlink function that calls the system readlink(1) if it exists. Otherwise it uses stat(1) to emulate the same functionality. In contrast to the functions in the previous section, you may pass -- as the first argument, since you may be calling the system readlink(1).

Quickstart

readlink -f does two things

1. resolves symlinks recursively
2. canonicalizes the result, hence:

realpath() {
    canonicalize_path "$(resolve_symlinks "$1")"
}
First, the symlink resolver implementation:

resolve_symlinks() {
    local dir_context path
    path=$(readlink -- "$1")
    if [ $? -eq 0 ]; then
        dir_context=$(dirname -- "$1")
        resolve_symlinks "$(_prepend_path_if_relative "$dir_context" "$path")"
    else
        printf '%s\n' "$1"
    fi
}

_prepend_path_if_relative() {
    case "$2" in
        /* ) printf '%s\n' "$2" ;;
         * ) printf '%s\n' "$1/$2" ;;
    esac 
}

Finally, the function for canonicalizing a path:

canonicalize_path() {
    if [ -d "$1" ]; then
        _canonicalize_dir_path "$1"
    else
        _canonicalize_file_path "$1"
    fi
}   

_canonicalize_dir_path() {
    (cd "$1" 2>/dev/null && pwd -P) 
}           

_canonicalize_file_path() {
    local dir file
    dir=$(dirname -- "$1")
    file=$(basename -- "$1")
    (cd "$dir" 2>/dev/null && printf '%s/%s\n' "$(pwd -P)" "$file")
}

quickstart source: stackoverflow

License

MIT