diff --git a/src/fd/fmt.cpp b/src/fd/fmt.cpp
index fc6392d..217949d 100644
--- a/src/fd/fmt.cpp
+++ b/src/fd/fmt.cpp
@@ -1,5 +1,8 @@
+#include <cstdlib>
 #include <stdplus/fd/fmt.hpp>
 #include <stdplus/fd/ops.hpp>
+#include <stdplus/util/cexec.hpp>
+#include <sys/stat.h>
 
 namespace stdplus
 {
@@ -32,5 +35,41 @@
     }
 }
 
+FormatToFile::FormatToFile(std::string_view tmpl) :
+    tmpname(tmpl),
+    fd(CHECK_ERRNO(mkstemp(tmpname.data()),
+                   [&](int error) {
+                       auto msg = fmt::format("mkstemp({})", tmpname);
+                       tmpname.clear();
+                       throw std::system_error(error, std::generic_category(),
+                                               msg);
+                   })),
+    buf(fd)
+{
+}
+
+FormatToFile::~FormatToFile()
+{
+    if (!tmpname.empty())
+    {
+        std::error_code ec;
+        std::filesystem::remove(tmpname, ec);
+    }
+}
+
+void FormatToFile::commit(const std::filesystem::path& out, int mode)
+{
+    {
+        buf.flush();
+        auto ifd = std::move(fd);
+    }
+    CHECK_ERRNO(chmod(tmpname.c_str(), mode), [&](int error) {
+        throw std::system_error(error, std::generic_category(),
+                                fmt::format("chmod({}, {})", tmpname, mode));
+    });
+    std::filesystem::rename(tmpname, out);
+    tmpname.clear();
+}
+
 } // namespace fd
 } // namespace stdplus