shader file call in .osg file


was wondering if anyone has got a shader to load and run from a .osg file (not strictly openGL).

in file had simple
code {
“void main (void)”
" gl_FragColor = vec4( 0.0, 0.0, 1.0, 1.0 );"

which does give me a blue shaded object as expected.
but tried to replace code with a blue.frag file
code {
file “blue.frag”
which does nothing, though it does appear the file is read, just does not apply itself.

so was wondering if other gl-language is needed other the just the file name?
such as using a file call on a texture which then needs futher parameters to work.

thank you Mr. D