For some obscure reason I have written a bash script which generates some source code, then compiles it, using
... whatever ... | gcc -x c -o /dev/stdout
Now, I want to execute the result on the compilation. How can I make that happen? No use of files please.
As Charles Duffy said, to execute a binary, you'd have to tell your operating system (which seems to be a Unix variant) to load and execute something – and Unix systems only take files to execute them directly.
What you could do is have a process that prepares a memory region containing the ELF binary, fork and jump into that region - but even that is questionable, considering that there's CPU support to suppress exactly that operation (R^X). Basically, what you need is a runtime linker, and shells do not (and also: should not) include something like that.
Let's drop the Bash requirement (which really just sounds like you're trying to find an obvious hole in an application that is older than I am grumpy):
Generally, requiring ELF (which is a file format) and avoiding files at the same time is a tad complicated. GCC generates machine code. If you just want to execute known machine code, put it into some buffer, build a function pointer to that and call it. Simple as that. However, you'd obviously don't have all the nice relocation and dynamic linking that the process of executing an ELF binary or loading a shared object (dlopen) would have.
If you want that, I'd look in the direction of things like LLVM – I know, for a fact, that there's people building "I compile C++ at runtime and execute it" with LLVM as executing instance, and clang as compiler. In the end, what your gcc|something is is really just JIT – an old technology :)