I am not asking to make golang do some sort of "eval" in the current context, just need it to take a input string (say, received from network) and execute it as a separate golang program.
In theory, when you run go run testme.go, it will read the content of testme.go into a string and parse, compile and execute it. Wonder if it is possible to call a go function to execute a string directly. Note that I have a requirement not to write the string into a file.
UPDATE1
I really want to find out if there is a function (in some go package) that serves as an entry point of go, in another word, I can call this function with a string as parameter, it will behave like go run testme.go, where testme.go has the content of that string.
AFAIK it cannot be done, and the go compiler has to write intermediate files, so even if you use go run and not go build, files are created for the sake of running the code, they are just cleaned up if necessary. So you can't run a go program without touching the disk, even if you manage to somehow make the compiler take the source not from a file.
For example, running strace on calling go run on a simple hello world program, shows among other things, the following lines:
mkdir("/tmp/go-build167589894", 0700)
// ....
mkdir("/tmp/go-build167589894/command-line-arguments/_obj/exe/", 0777)
// ... and at the end of things
unlink("/tmp/go-build167589894/command-line-arguments/_obj/exe/foo")
// ^^^ my program was called foo.go
// ....
// and eventually:
rmdir("/tmp/go-build167589894")
So you can see that go run does a lot of disk writing behind the scenes, just cleans up afterwards.
I suppose you can mount some tmpfs and build in it if you wish, but otherwise I don't believe it's possible.