Finding supported GLSL version

There's a specific mapping between OpenGL version and supported GLSL version:

GLSL Version      OpenGL Version
1.10              2.0
1.20              2.1
1.30              3.0
1.40              3.1
1.50              3.2
3.30              3.3
4.00              4.0
4.10              4.1
4.20              4.2
4.30              4.3
4.40              4.4
4.50              4.5

There's a well defined API for querying the OpenGL version. Use the table above for mapping to GLSL versions (after OpenGL-3.3 it's very logical).

Furthermore the specification defines the format of the GL_VERSION and GL_SHADING_LANGUAGE_VERSION to

begin with a version number. The version number uses one of these forms:

major_number.minor_number | major_number.minor_number.release_number