Programming

it is possible for getenv() to return null! Test for that case or strcat will crash in it!

Writing CGI scripts in C is kind of clumsy. You can artificially create the environment your application expects when running it in GDB.

Create the environment variables for the application that apache would usually set up. You would only need to create the environment variables that your application requires. Thus, when you run GDB make an environment variable to simulate apache.

Code:

$ export DOCUMENT_ROOT="foo"
$ gdb myscript.cgi

The output will be ugly because it will be spitting out HTML.

Indeed. You should do as Corona688 has said.

Code:

char *p;
if( !( p = getenv( "DOCUMENT_ROOT" ) ) ) {
  // Do something
}
else
  strcat(DOCUMENTROOT, p);

You should also make sure p is not larger than DOCUMENTROOT or you shall cause a buffer overflow.