ffi issues

[sakulstra]

Hello,
I wrote a foundry script with essentially logs some storage to a file, before and after the execution of some commands.
Afterwards i want to diff these two files, which works just fine via Makefile:

git-diff :
	@printf '%s\n%s\n%s\n' "\`\`\`diff" "$$(git diff --no-index --diff-algorithm=patience --ignore-space-at-eol ${before} ${after})" "\`\`\`" > diffs/${out}.md

Now i noticed that doing this, after the script execution is a bit cumbersome and i'd rather have the diffing be part of the foundry script, but I simply can't manage to.

I tried to essentially execute the whole command via ffi which threw a gazillion of rather weird errors(https://book.getfoundry.sh/cheatcodes/ffi?highlight=ffi#ffi).

So I tried reducing complexity to sth like printf hello > test.txt just to see if it works in general:

function testFfi() public {
    string[] memory inputs = new string[](4);
    inputs[0] = 'printf';
    inputs[1] = 'hello';
    inputs[2] = '>';
    inputs[3] = 'test.txt';

    vm.ffi(inputs);
  }

Which yields 2023-02-02T16:56:28.504122Z ERROR foundry_evm::executor::inspector::cheatcodes::ext: stderr err="printf: warning: ignoring excess arguments, starting with ‘>’\n".

Is there any way to do what i want to do via foundry?
Essentially I want to exec a command without caring for the response, so perhaps ffi might not be the correct tool for the job.

[DaniPopes]

The > text.txt is not part of the call to printf, it's a sh builtin: you're executing the command printf with 3 arguments, which fails. Same goes for expansions: $(...)
You would have to wrap the printf with a sh / bash command like so:
sh -c "printf hello > test.txt":

string[] memory inputs = new string[](4);
inputs[0] = "sh";
inputs[1] = "-c";
inputs[2] = "printf hello > test.txt";
vm.ffi(inputs);