Support for $XDG_DATA_HOME was added in a recent release, however it is not used under macOS and falls back to the default location ~/Library/Application Support.

fnm 1.29.1

mv ~/.fnm ~/.local/share/fnm
fnm env
# FNM_DIR -> ~/Library/Application Support/fnm

However $XDG_DATA_HOME is respected under Linux.

# macOS
XDG_DATA_HOME=/tmp fnm env
# FNM_DIR -> ~/Library/Application Support/fnm

# Linux
XDG_DATA_HOME=/tmp fnm env
# FNM_DIR -> /tmp/fnm

The XDG_DATA_HOME environment variable should be used first if it is configured, and then fall back to the macOS location.

For example, the changes to the install script in Pull Request 614.

#614

if [ -d "$HOME/.fnm" ]; then
  INSTALL_DIR="$HOME/.fnm"
elif [ ! -z $XDG_DATA_HOME ]; then
  INSTALL_DIR="$XDG_DATA_HOME/fnm"
elif [ "$OS" = "Darwin" ]; then
  INSTALL_DIR="$HOME/Library/Application Support/fnm"
  # ...
fi