Make clear command work without explicit session argument

When run inside a session, `atch clear` now defaults to clearing
the current session's log by reading the ATCH_SESSION environment
variable. For nested sessions, it clears the innermost session.

Author: arthurpro

README.md

@@ -82,7 +82,7 @@ If no command is given, `$SHELL` is used.
 | `run <session> [cmd...]` | Like `start`, but atch stays in the foreground instead of daemonizing. |
 | `push <session>` | Copy stdin verbatim to the session. |
 | `kill [-f] <session>` | Gracefully stop a session (SIGTERM, then SIGKILL after 5 s if needed). With `-f` / `--force`, skip the grace period and send SIGKILL immediately. |
-| `clear <session>` | Truncate the on-disk session log. |
+| `clear [<session>]` | Truncate the on-disk session log. Defaults to the current session when run inside one. |
 | `list` | List all sessions. Shows `[attached]` when a client is connected, `[stale]` for leftover sockets with no running master. Prints `(no sessions)` when the list is empty. |
 | `current` | Print the current session name and exit 0 if inside a session; exit 1 silently if not. |
 
@@ -241,7 +241,7 @@ Every byte written to the pty is appended to a log file on disk
 This is fundamentally different from `tmux`, `screen`, and `dtach`: they hold
 history only in memory. When the process exits or the machine restarts, the
 output is gone. With `atch` the raw byte stream is on disk until you
-explicitly clear it with `atch clear <session>`.
+explicitly clear it with `atch clear` (or `atch clear <session>`).
 
 The log is capped at 1 MB by default; once it exceeds that, only the most
 recent 1 MB is kept. You can change the cap per session with `-C`:
@@ -286,7 +286,8 @@ The value must be a power of two.
 To wipe the on-disk log and start clean on the next attach:
 
 ```sh
-atch clear mysession
+atch clear            # inside a session — clears the current session's log
+atch clear mysession  # from outside — clear a named session's log
 ```
 
 ## Backward compatibility

atch.c

@@ -507,8 +507,22 @@ static int cmd_clear(int argc, char **argv)
 	char log_path[600];
 	int fd;
 
-	if (consume_session(&argc, &argv))
-		return 1;
+	if (argc > 0) {
+		if (consume_session(&argc, &argv))
+			return 1;
+	} else {
+		const char *chain = getenv(SESSION_ENVVAR);
+		const char *last;
+
+		if (!chain || !*chain) {
+			printf("%s: No session was specified.\n", progname);
+			printf("Try '%s --help' for more information.\n",
+			       progname);
+			return 1;
+		}
+		last = strrchr(chain, ':');
+		sockname = (char *)(last ? last + 1 : chain);
+	}
 	if (argc > 0) {
 		printf("%s: Invalid number of arguments.\n", progname);
 		printf("Try '%s --help' for more information.\n", progname);
@@ -579,7 +593,7 @@ static void usage(void)
 	       "  kill    [-f] <session>"
 	       "\t\tStop session (SIGTERM then SIGKILL)\n"
 	       "    -f, --force\t\t\tSkip grace period, send SIGKILL immediately\n"
-	       "  clear   <session>"
+	       "  clear   [<session>]"
 	       "\t\t\tTruncate the session log\n"
 	       "  list\t\t\t\t\tList all sessions\n"
 	       "  current\t\t\t\tPrint current session name\n"

tests/test.sh

@@ -250,8 +250,8 @@ assert_contains "kill -f: nonexistent → message"     "does not exist" "$out"
 # ── 6. clear command ─────────────────────────────────────────────────────────
 
 run "$ATCH" clear
-assert_exit     "clear: no session → exit 1"         1 "$rc"
-assert_contains "clear: no session → message"        "No session was specified" "$out"
+assert_exit     "clear: no session, no env → exit 1"         1 "$rc"
+assert_contains "clear: no session, no env → message"        "No session was specified" "$out"
 
 # clear a nonexistent log is silent success
 run "$ATCH" clear s-noexist-clear
@@ -279,6 +279,24 @@ run "$ATCH" clear s-noexist-clear extra
 assert_exit     "clear: extra arg → exit 1"          1 "$rc"
 assert_contains "clear: extra arg → message"         "Invalid number of arguments" "$out"
 
+# atch clear with ATCH_SESSION set uses current session
+"$ATCH" start s-clear-cur sleep 999
+wait_socket s-clear-cur
+run env ATCH_SESSION="$HOME/.cache/atch/s-clear-cur" "$ATCH" clear
+assert_exit     "clear: current session → exit 0"    0 "$rc"
+assert_contains "clear: current session → message"   "log cleared" "$out"
+
+# atch clear with no arg uses innermost session from nested chain
+"$ATCH" start s-clear-inner sleep 999
+wait_socket s-clear-inner
+run env ATCH_SESSION="$HOME/.cache/atch/s-clear-cur:$HOME/.cache/atch/s-clear-inner" \
+        "$ATCH" clear
+assert_exit     "clear: nested env no arg → exit 0"  0 "$rc"
+assert_contains "clear: nested env no arg → message" "s-clear-inner" "$out"
+
+tidy s-clear-cur
+tidy s-clear-inner
+
 # ── 7. current command ───────────────────────────────────────────────────────
 
 run "$ATCH" current