Shaders and Programs - Praise for OpenGL ES 30 Programming Guide - page 72

Calling glCompileShader will cause the shader source code that has
been stored in the shader object to be compiled. As with any normal
language compiler, the first thing you want to know after compiling is
whether there were any errors. You can use glGetShaderiv to query
for this information, along with other information about the shader
object.

void glGetShaderiv (GLuint shader , GLenum pname ,
GLint *params )

handle to the shader object to get information about

shader

the parameter to get information about; can be
GL_COMPILE_STATUS
GL_DELETE_STATUS
GL_INFO_LOG_LENGTH
GL_SHADER_SOURCE_LENGTH
GL_SHADER_TYPE

pname

pointer to integer storage location for the result of the query

params

To check whether a shader has compiled successfully, you can call
glGetShaderiv on the shader object with the GL_COMPILE_STATUS
argument for pname . If the shader compiled successfully, the result
will be GL_TRUE . If the shader failed to compile, the result will be
GL_FALSE . If the shader does fail to compile, the compile errors will be
written into the info log. The info log is a log written by the compiler
that contains any error messages or warnings. It can be written with
information even if the compile operation is successful. To check the
info log, its length can be queried using GL_INFO_LOG_LENGTH . The
info log itself can be retrieved using glGetShaderInfoLog (described
next). Querying for GL_SHADER_TYPE will return whether the shader
is a GL_VERTEX_SHADER or GL_FRAGMENT_SHADER . Querying for
GL_SHADER_SOURCE_LENGTH returns the length of the shader source
code, including the null terminator. Finally, querying for GL_DELETE_
STATUS returns whether the shader has been marked for deletion using
glDeleteShader .

After compiling the shader and checking the info log length, you might
want to retrieve the info log (especially if compilation failed, to find out
why). To do so, you first need to query for the GL_INFO_LOG_LENGTH and
allocate a string with sufficient storage to store the info log. The info log
can then be retrieved using glGetShaderInfoLog .