1 files changed, 11 insertions, 0 deletions
diff --git a/src/host_io.zig b/src/host_io.zig
index 1fab3729..8ddb0c90 100644
--- a/src/host_io.zig
+++ b/src/host_io.zig
@@ -1351,6 +1351,14 @@ test "the child environment replaces the launcher's terminal identity exactly on
 
 extern "c" fn unsetenv(name: [*:0]const u8) c_int;
 
+fn exportWinid(serial: u32) void {
+    var buf: [16]u8 = undefined;
+    if (serial != 0) if (std.fmt.bufPrintSentinel(&buf, "{d}", .{serial}, 0)) |text| {
+        if (Shell.setenv("winid", text, 1) == 0) return;
+    } else |_| {};
+    _ = unsetenv("winid");
+}
+
 /// The longest line a command pane runs (exec.zig refuses a longer one).
 pub const exec_command_max = pardes.exec.command_max;
 
@@ -1418,6 +1426,9 @@ pub fn forkShell(
         if (core) |c| (if (c.panes[pane]) |pn| pn.serial else 0) else 0,
         if (core) |c| !c.opts.nested else false,
     );
+    // acme's `$winid`: the pane a command was run from, so a script it runs
+    // can address that pane; unset for a shell and a header tag's command.
+    exportWinid(if (core) |c| (if (c.panes[pane]) |pn| (if (pn.command != null) pn.command_from else 0) else 0) else 0);
     if (helper) |path| {
         const c = core.?;
         const pn = c.panes[pane].?;