Use realpath of scripts to determine relative locations (#308)

Just using paths relative to ${BASH_SOURCE} to access `libexec`
fails if the scripts are symlinked to a location,
such as when installed with Homebrew,
since the `libexec` directory is not linked into `brew --prefix`.

Implement a simple version of `realpath`
and run `${BASH_SOURCE}` through it.
This gets the actual installation directory
relative to which `libexec` is located.

Co-authored-by: Andrew Christianson <achristianson@edmunds.com>

bin/pyenv-virtualenv-prefix

@@ -6,7 +6,21 @@
 
 set -e
 [ -n "$PYENV_DEBUG" ] && set -x
-. "${BASH_SOURCE%/*}"/../libexec/pyenv-virtualenv-realpath
+if [ -L "${BASH_SOURCE}" ]; then
+    READLINK=$(type -p greadlink readlink | head -1)
+    if [ -z "$READLINK" ]; then
+        echo "pyenv: cannot find readlink - are you missing GNU coreutils?" >&2
+        exit 1
+    fi
+    resolve_link() {
+        $READLINK -f "$1"
+    }
+    script_path=$(resolve_link ${BASH_SOURCE})
+else
+    script_path=${BASH_SOURCE}
+fi
+
+. ${script_path%/*}/../libexec/pyenv-virtualenv-realpath
 
 if [ -z "$PYENV_ROOT" ]; then
   PYENV_ROOT="${HOME}/.pyenv"

bin/pyenv-virtualenvs

@@ -7,7 +7,21 @@
 
 set -e
 [ -n "$PYENV_DEBUG" ] && set -x
-. "${BASH_SOURCE%/*}"/../libexec/pyenv-virtualenv-realpath
+if [ -L "${BASH_SOURCE}" ]; then
+    READLINK=$(type -p greadlink readlink | head -1)
+    if [ -z "$READLINK" ]; then
+        echo "pyenv: cannot find readlink - are you missing GNU coreutils?" >&2
+        exit 1
+    fi
+    resolve_link() {
+        $READLINK -f "$1"
+    }
+    script_path=$(resolve_link ${BASH_SOURCE})
+else
+    script_path=${BASH_SOURCE}
+fi
+
+. ${script_path%/*}/../libexec/pyenv-virtualenv-realpath
 
 if [ -z "$PYENV_ROOT" ]; then
   PYENV_ROOT="${HOME}/.pyenv"