GDL (GNU Data Language) is a free/libre open-source program that runs most IDL code. GDL is actively developed on GitHub. GDL is easily installed by:

• Linux: apt install gnudatalanguage
• macOS Homebrew: brew install gnudatalanguage
• Windows: get the latest release

If you choose to build GDL source use the GDL build script “scripts/build_gdl.sh” to get the prerequisites. If Anaconda Python is present, conda deactivate first to avoid library problems when building GDL.

cmake -B build --install-prefix=$HOME/gdl

cmake --build build --parallel

(optional) Check the install. You will see several plots appearing and disappearing automatically during this test, which takes a few minutes.

cmake --test-dir build -V

Install (do not use sudo):

cmake --install build

Do not build on an ExFAT / FAT32 drive, as the build will fail since symbolic links are not allowed on ExFAT / FAT32. If cmake reports libeigen being too old, read below to the optional LibEigen3 section, or use -DEIGEN3=OFF If you wish to use your Linux repo’s older version of IDL, just use /usr/local/bin/gdl or similar, or rename ~/.local/bin/gdl to ~/.local/bin/gdl0.98 or similar.

Troubleshooting build:

• Runtime search path conflicts: temporarily comment out those paths in ~/.profile (typically from Anaconda Python, libreadline, libhistory, libz, libjpeg.so)
• Problems with LZMA, try disabling HDF5: cmake -DHDF5=OFF