1 files changed, 52 insertions, 0 deletions
diff --git a/nihil.posix/find_in_path.cc b/nihil.posix/find_in_path.cc
new file mode 100644
index 0000000..7b03faa
--- /dev/null
+++ b/nihil.posix/find_in_path.cc
@@ -0,0 +1,52 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <filesystem>
+#include <optional>
+#include <ranges>
+#include <string>
+
+#include <fcntl.h>
+#include <paths.h>
+#include <unistd.h>
+
+module nihil.posix;
+
+namespace nihil {
+
+auto find_in_path(std::filesystem::path const &file) -> std::optional<std::filesystem::path>
+{
+	using namespace std::literals;
+
+	auto try_return = [](std::filesystem::path file)
+		-> std::optional<std::filesystem::path>
+	{
+		auto ret = ::access(file.string().c_str(), X_OK);
+		if (ret == 0)
+			return {std::move(file)};
+		return {};
+	};
+
+	// Absolute pathname skips the search.
+	if (file.is_absolute())
+		return try_return(file);
+
+	auto path = getenv("PATH").value_or(_PATH_DEFPATH);
+
+	for (auto &&dir : path | std::views::split(':')) {
+		// An empty $PATH element means cwd.
+		auto sdir = dir.empty()
+			? std::filesystem::path(".")
+			: std::filesystem::path(std::string_view(dir));
+
+		if (auto ret = try_return(sdir / file); ret)
+			return ret;
+	}
+
+	return {};
+}
+
+} // namespace nihil