While GDL has CMSvlib installed to read / write IDL .sav files, here is how to install CMSvlib if desired.

Download CMSVlib and extract to “~/.local/share/cmsvlib”. Add line to ~/.profile:

export GDL_STARTUP=$HOME/.gdl/gdl-startup.pro

Copy and paste into  “~/.gdl/gdl-startup.pro”

!PATH=!PATH+':'+Expand_Path('+~/.local/share/cmsvlib/')

Reopen Terminal and GDL. Load IDL .sav file like:

restore,'myfile.sav'

Check GDL paths loaded:

print,!PATH