From 77571a29fd7e6d41a5c15da9f7fdf10e1e63e752 Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Sun, 10 May 2026 11:02:29 +0100
Subject: [PATCH 1/9] feat: add collapsable output (wip)

---
 src/mdb/mdb_shell.py |  3 ++-
 src/mdb/utils.py     | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/src/mdb/mdb_shell.py b/src/mdb/mdb_shell.py
index 657c2b2..9713914 100644
--- a/src/mdb/mdb_shell.py
+++ b/src/mdb/mdb_shell.py
@@ -24,6 +24,7 @@
     parse_ranks,
     pretty_print_response,
     sort_debug_response,
+    reduce_response,
 )
 
 if TYPE_CHECKING:
@@ -214,7 +215,7 @@ def ask_remain_calm(signame: str) -> None:
 
         if command_response.msg_type == "exchange_command_response":
             response = sort_debug_response(command_response.data["results"])
-            pretty_print_response(response)
+            reduce_response(response)
         else:
             print("Received unexpected message type: %s", command_response.msg_type)
         return
diff --git a/src/mdb/utils.py b/src/mdb/utils.py
index 3ac7f88..6a45de1 100644
--- a/src/mdb/utils.py
+++ b/src/mdb/utils.py
@@ -4,6 +4,7 @@
 import re
 from os.path import expanduser
 from typing import TYPE_CHECKING
+from collections import defaultdict
 
 if TYPE_CHECKING:
     from .backend import DebugBackend
@@ -21,6 +22,29 @@ def sort_debug_response(results: dict[int, str]) -> dict[int, str]:
     return dict(sorted(results.items()))
 
 
+def collapse_ranges(values: list[int]) -> str:
+    """Collapse a list of integers into minimal range notation.
+
+    e.g. [1, 2, 3, 6, 7, 10, 11, 12] -> '1-3,6-7,10-12'
+    """
+    sorted_vals = sorted(set(values))
+    if not sorted_vals:
+        return ""
+
+    ranges = []
+    start = end = sorted_vals[0]
+
+    for n in sorted_vals[1:]:
+        if n == end + 1:
+            end = n
+        else:
+            ranges.append(f"{start}-{end}" if start != end else str(start))
+            start = end = n
+
+    ranges.append(f"{start}-{end}" if start != end else str(start))
+    return ",".join(ranges)
+
+
 def pretty_print_response(response: dict[int, str]) -> None:
     lines = []
     for rank, result in response.items():
@@ -30,6 +54,23 @@ def pretty_print_response(response: dict[int, str]) -> None:
     print(combined_output)
 
 
+def reduce_response(response: dict[int, str]) -> None:
+    """
+    """
+    reduced = defaultdict(list)
+    for rank, result in response.items():
+        if result:
+            for line in result.split("\r\n")[1:-1]:
+                reduced[line].append(rank)
+
+    reduced = {k: collapse_ranges(v) for k, v in reduced.items()}
+
+    max_len = max([len(v) for v in reduced.values()], default=0)
+    for line, ranks_str in reduced.items():
+        padded = ranks_str.rjust(max_len)
+        print(f"{padded}: {line}")
+
+
 def extract_float(line: str, backend: "DebugBackend") -> float:
     float_regex = backend.float_regex
     line = strip_control_characters(line)

From 963d1a9d594a128fb88ea2a61e9387102e1e9c5a Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Sun, 10 May 2026 18:40:04 +0100
Subject: [PATCH 2/9] feat: allow user to switch between pretty and reduced
 output

---
 src/mdb/mdb_shell.py | 39 ++++++++++++++++++++++++++++++++++++++-
 src/mdb/utils.py     | 34 ++++++++++++++++++++++++++++++++--
 2 files changed, 70 insertions(+), 3 deletions(-)

diff --git a/src/mdb/mdb_shell.py b/src/mdb/mdb_shell.py
index 9713914..c7393c1 100644
--- a/src/mdb/mdb_shell.py
+++ b/src/mdb/mdb_shell.py
@@ -56,6 +56,7 @@ def __init__(self, shell_opts: ShellOpts, client: Client) -> None:
         self.exchange_select = parse_ranks(self.exchange_select_str)
         self.select_str = self.exchange_select_str
         self.select = self.exchange_select
+        self.output_mode = "reduce"  # 'pretty' or 'reduce'
         backend_name = shell_opts["backend_name"].lower()
         if backend_name in backends:
             self.backend = backends[backend_name]()
@@ -215,7 +216,10 @@ def ask_remain_calm(signame: str) -> None:
 
         if command_response.msg_type == "exchange_command_response":
             response = sort_debug_response(command_response.data["results"])
-            reduce_response(response)
+            if self.output_mode == "reduce":
+                reduce_response(response)
+            else:
+                pretty_print_response(response)
         else:
             print("Received unexpected message type: %s", command_response.msg_type)
         return
@@ -251,6 +255,39 @@ def do_shell(self, line: str) -> None:
         run(split(line))
         return
 
+    def do_set(self, line: str) -> None:
+        """
+        Description:
+        Set mdb options.
+
+        Example:
+        Switch output format between pretty-printed and reduced (deduplicated) mode:
+
+            (mdb) set output pretty
+            (mdb) set output reduce
+
+        Show current settings:
+
+            (mdb) set
+        """
+        if not line:
+            print(f"output: {self.output_mode}")
+            return
+
+        parts = line.split()
+        if len(parts) < 2:
+            print("Usage: set output [pretty|reduce]")
+            return
+
+        if parts[0].lower() == "output":
+            mode = parts[1].lower()
+            if mode in ("pretty", "reduce"):
+                self.output_mode = mode
+            else:
+                print(f"Error: unknown output mode '{mode}'. Use 'pretty' or 'reduce'.")
+        else:
+            print(f"Error: unknown option '{parts[0]}'. Use 'output'.")
+
     def do_select(self, line: str) -> None:
         """
         Description:
diff --git a/src/mdb/utils.py b/src/mdb/utils.py
index 6a45de1..5dac63b 100644
--- a/src/mdb/utils.py
+++ b/src/mdb/utils.py
@@ -55,7 +55,37 @@ def pretty_print_response(response: dict[int, str]) -> None:
 
 
 def reduce_response(response: dict[int, str]) -> None:
-    """
+    """Reduce debug output by deduplicating common lines across ranks.
+
+    Parses each rank's output, groups identical lines together, and prints
+    each unique line prefixed by the collapsed set of ranks that produced it.
+    Lines from only one rank appear normally; shared lines are printed once
+    with all contributing ranks.
+
+    Example output before and after:
+
+        Before (raw output per rank):
+
+            0:      process 45402
+            0:      cmdline = '/mdb/examples/simple-mpi.exe'
+            0:      cwd = '/mdb'
+            0:      exe = '/mdb/examples/simple-mpi.exe'
+            ************************************************************************
+            1:      process 45403
+            1:      cmdline = '/mdb/examples/simple-mpi.exe'
+            1:      cwd = '/mdb'
+            1:      exe = '/mdb/examples/simple-mpi.exe'
+
+        After (deduplicated, ranks collapsed):
+
+              0: process 45402
+            0-1: cmdline = '/mdb/examples/simple-mpi.exe'
+            0-1: cwd = '/mdb'
+            0-1: exe = '/mdb/examples/simple-mpi.exe'
+              1: process 45403
+
+    Args:
+        response: dict mapping process rank (int) to its output string.
     """
     reduced = defaultdict(list)
     for rank, result in response.items():
@@ -91,7 +121,7 @@ def extract_float(line: str, backend: "DebugBackend") -> float:
 
 def prepend_ranks(rank: int, result: str) -> str:
     return "".join(
-        [f"{rank}:\t" + line + "\r\n" for line in result.split("\r\n")[1:-1]]
+        [f"{rank}: " + line + "\r\n" for line in result.split("\r\n")[1:-1]]
     )
 
 

From bf3710a9349789d587143d203f0d4e3e4673f19e Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Sun, 10 May 2026 18:40:39 +0100
Subject: [PATCH 3/9] test: add new test and update existing tests to reflect
 new reduce output

---
 tests/output/answer-gdb.stdout  |  77 +++++++-----------
 tests/output/answer-lldb.stdout | 138 ++++++++++++--------------------
 tests/test_utils.py             |  79 +++++++++++++++++-
 3 files changed, 159 insertions(+), 135 deletions(-)

diff --git a/tests/output/answer-gdb.stdout b/tests/output/answer-gdb.stdout
index ac72227..e6e9cb1 100644
--- a/tests/output/answer-gdb.stdout
+++ b/tests/output/answer-gdb.stdout
@@ -1,57 +1,36 @@
 hello
-0:cmdline = simple-mpi.exe
-0:cwd = [mdb root]
-0:exe = simple-mpi.exe
-************************************************************************
-1:cmdline = simple-mpi.exe
-1:cwd = [mdb root]
-1:exe = simple-mpi.exe
-0:Breakpoint 2 at [hex address]: file simple-mpi.f90, line 15.
-************************************************************************
-1:Breakpoint 2 at [hex address]: file simple-mpi.f90, line 15.
-0:Breakpoint 3 at [hex address]: file simple-mpi.f90, line 17.
-************************************************************************
-1:Breakpoint 3 at [hex address]: file simple-mpi.f90, line 17.
-0:Continuing.
+0-1: cmdline = simple-mpi.exe
+0-1: cwd = [mdb root]
+0-1: exe = simple-mpi.exe
+0-1: Breakpoint 2 at [hex address]: file simple-mpi.f90, line 15.
+0-1: Breakpoint 3 at [hex address]: file simple-mpi.f90, line 17.
+0-1: Continuing.
+0-1:
+0-1: Thread 1 "simple-mpi.exe" hit Breakpoint 2, simple () at simple-mpi.f90:15
+0-1: 15  var = 10.*process_rank
+0: Continuing.
 0:
-0:Thread 1 "simple-mpi.exe" hit Breakpoint 2, simple () at simple-mpi.f90:15
-0:15  var = 10.*process_rank
-************************************************************************
-1:Continuing.
-1:
-1:Thread 1 "simple-mpi.exe" hit Breakpoint 2, simple () at simple-mpi.f90:15
-1:15  var = 10.*process_rank
-0:Continuing.
-0:
-0:Thread 1 "simple-mpi.exe" hit Breakpoint 3, simple () at simple-mpi.f90:17
-0:17  if (process_rank == 0) then
-0:#0  simple () at simple-mpi.f90:17
-************************************************************************
-1:#0  simple () at simple-mpi.f90:15
+0: Thread 1 "simple-mpi.exe" hit Breakpoint 3, simple () at simple-mpi.f90:17
+0: 17  if (process_rank == 0) then
+0: #0  simple () at simple-mpi.f90:17
+1: #0  simple () at simple-mpi.f90:15
 unrecognized command [made-up-command]. Type help to find out list of possible commands.
 Error: user specified option [select] must be subset of available ranks (check mdb launch command).
 select = [10] but available ranks are [0-1].
-1:Continuing.
+1: Continuing.
 1:
-1:Thread 1 "simple-mpi.exe" hit Breakpoint 3, simple () at simple-mpi.f90:17
-1:17  if (process_rank == 0) then
+1: Thread 1 "simple-mpi.exe" hit Breakpoint 3, simple () at simple-mpi.f90:17
+1: 17  if (process_rank == 0) then
 File [deliberately-missing-file.mdb] not found. Please check the file exists and try again.
-0:25
-************************************************************************
-1:25
-0:Continuing.
-0:           1 s...
-0:           2 s...
-0:           3 s...
-0: in level 1
-0: in level 2
-0: internal process:            0 of            2
-0: var =    0.00000000
-************************************************************************
-1:Continuing.
-1: in level 1
-1: in level 2
-1: internal process:            1 of            2
-1: var =    10.0000000
-************************************************************************
+0-1: 25
+0-1: Continuing.
+  0:            1 s...
+  0:            2 s...
+  0:            3 s...
+0-1:  in level 1
+0-1:  in level 2
+  0:  internal process:            0 of            2
+  0:  var =    0.00000000
+  1:  internal process:            1 of            2
+  1:  var =    10.0000000
 exiting mdb...
\ No newline at end of file
diff --git a/tests/output/answer-lldb.stdout b/tests/output/answer-lldb.stdout
index ca6d5fb..82b0433 100644
--- a/tests/output/answer-lldb.stdout
+++ b/tests/output/answer-lldb.stdout
@@ -1,89 +1,57 @@
 hello
-0:* thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 1.1
-0:    frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:24:7
-0:   21    int process_rank, size_of_cluster;
-0:   22    float var;
-0:   23
-0:-> 24    var = 0.;
-0:          ^
-0:   25
-0:   26    MPI_Init(NULL, NULL);
-0:   27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
-************************************************************************
-1:* thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 1.1
-1:    frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:24:7
-1:   21    int process_rank, size_of_cluster;
-1:   22    float var;
-1:   23
-1:-> 24    var = 0.;
-1:          ^
-1:   25
-1:   26    MPI_Init(NULL, NULL);
-1:   27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
-0:Breakpoint 2: where = simple-mpi-cpp.exe`main + 95 at simple-mpi-cpp.cpp:30:12, address = [hex address]
-************************************************************************
-1:Breakpoint 2: where = simple-mpi-cpp.exe`main + 95 at simple-mpi-cpp.cpp:30:12, address = [hex address]
-0:Breakpoint 3: where = simple-mpi-cpp.exe`main + 127 at simple-mpi-cpp.cpp:32:20, address = [hex address]
-************************************************************************
-1:Breakpoint 3: where = simple-mpi-cpp.exe`main + 127 at simple-mpi-cpp.cpp:32:20, address = [hex address]
-0:* thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
-0:    frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
-0:   27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
-0:   28    MPI_Comm_rank(MPI_COMM_WORLD, &process_rank);
-0:   29
-0:-> 30    var = 10.*process_rank;
-0:               ^
-0:   31
-0:   32    if (process_rank == 0){
-************************************************************************
-1:* thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
-1:    frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
-1:   27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
-1:   28    MPI_Comm_rank(MPI_COMM_WORLD, &process_rank);
-1:   29
-1:-> 30    var = 10.*process_rank;
-1:               ^
-1:   31
-1:   32    if (process_rank == 0){
-0:* thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 3.1
-0:    frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:32:20
-0:   29
-0:   30    var = 10.*process_rank;
-0:   31
-0:-> 32    if (process_rank == 0){
-0:                       ^
-0:   34
-0:   35      for (int i = 0; i < 3; ++i) {
-0:* thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 3.1
-0:    frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:32:20
-************************************************************************
-1:* thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
-1:    frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
+0-1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 1.1
+0-1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:24:7
+0-1:    21    int process_rank, size_of_cluster;
+0-1:    22    float var;
+0-1:    23
+0-1: -> 24    var = 0.;
+0-1:           ^
+0-1:    25
+0-1:    26    MPI_Init(NULL, NULL);
+0-1:    27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
+0-1: Breakpoint 2: where = simple-mpi-cpp.exe`main + 95 at simple-mpi-cpp.cpp:30:12, address = [hex address]
+0-1: Breakpoint 3: where = simple-mpi-cpp.exe`main + 127 at simple-mpi-cpp.cpp:32:20, address = [hex address]
+0-1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
+0-1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
+0-1:    27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
+0-1:    28    MPI_Comm_rank(MPI_COMM_WORLD, &process_rank);
+0-1:    29
+0-1: -> 30    var = 10.*process_rank;
+0-1:                ^
+0-1:    31
+0-1:    32    if (process_rank == 0){
+0: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 3.1
+0:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:32:20
+0:    29
+0:    30    var = 10.*process_rank;
+0:    31
+0: -> 32    if (process_rank == 0){
+0:                        ^
+0:    34
+0:    35      for (int i = 0; i < 3; ++i) {
+0: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 3.1
+0:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:32:20
+1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
+1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
 unrecognized command [made-up-command]. Type help to find out list of possible commands.
-1:* thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 3.1
-1:    frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:32:20
-1:   29
-1:   30    var = 10.*process_rank;
-1:   31
-1:-> 32    if (process_rank == 0){
-1:                       ^
-1:   34
-1:   35      for (int i = 0; i < 3; ++i) {
+1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 3.1
+1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:32:20
+1:    29
+1:    30    var = 10.*process_rank;
+1:    31
+1: -> 32    if (process_rank == 0){
+1:                        ^
+1:    34
+1:    35      for (int i = 0; i < 3; ++i) {
 File [deliberately-missing-file.mdb] not found. Please check the file exists and try again.
-0:(int) 25
-************************************************************************
-1:(int) 25
-0:0 s...
-0:1 s...
-0:2 s...
-0:in level 1
-0:in level 2
-0:internal process: 0 of 2
-0:var = 0
-************************************************************************
-1:in level 1
-1:in level 2
-1:internal process: 1 of 2
-1:var = 10
-************************************************************************
+0-1: (int) 25
+  0: 0 s...
+  0: 1 s...
+  0: 2 s...
+0-1: in level 1
+0-1: in level 2
+  0: internal process: 0 of 2
+  0: var = 0
+  1: internal process: 1 of 2
+  1: var = 10
 exiting mdb...
\ No newline at end of file
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 8dc9cac..a840e00 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -1,7 +1,14 @@
 # Copyright 2023-2026 Tom Meltzer. See the top-level COPYRIGHT file for
 # details.
 
-from mdb.utils import parse_ranks, strip_bracketted_paste, strip_control_characters
+from mdb.utils import (
+    collapse_ranges,
+    parse_ranks,
+    pretty_print_response,
+    reduce_response,
+    strip_bracketted_paste,
+    strip_control_characters,
+)
 
 
 def test_parse_ranks() -> None:
@@ -18,6 +25,76 @@ def test_parse_ranks() -> None:
     assert ranks == [2, 3, 4]
 
 
+def test_collapse_ranges() -> None:
+    # consecutive integers collapse to a range
+    assert collapse_ranges([1, 2, 3, 4]) == "1-4"
+
+    # single integer
+    assert collapse_ranges([5]) == "5"
+
+    # multiple disjoint ranges
+    assert collapse_ranges([1, 2, 3, 6, 7, 10, 11, 12]) == "1-3,6-7,10-12"
+
+    # unsorted input is sorted internally
+    assert collapse_ranges([12, 10, 11, 7, 6, 3, 2, 1]) == "1-3,6-7,10-12"
+
+    # duplicates are deduplicated
+    assert collapse_ranges([1, 1, 2, 2, 3]) == "1-3"
+
+    # empty list returns empty string
+    assert collapse_ranges([]) == ""
+
+    # gaps between single values
+    assert collapse_ranges([1, 3, 5, 7]) == "1,3,5,7"
+
+    # mix of single values and ranges
+    assert collapse_ranges([1, 2, 5, 6, 7, 10]) == "1-2,5-7,10"
+
+
+def test_pretty_print_response(capsys) -> None:
+    response = {
+        0: "command ran\r\nline 1\r\nline 2\r\n",
+        1: "command ran\r\nline 3\r\n",
+    }
+    pretty_print_response(response)
+    captured = capsys.readouterr()
+
+    assert "0: line 1" in captured.out
+    assert "0: line 2" in captured.out
+    assert "1: line 3" in captured.out
+    assert "*" * 72 in captured.out  # separator between ranks
+    # header lines are skipped
+    assert "command ran" not in captured.out
+
+
+def test_reduce_response(capsys) -> None:
+    response = {
+        0: "header\r\ncommon line\r\nunique to 0\r\n",
+        1: "header\r\ncommon line\r\nunique to 1\r\n",
+        2: "header\r\ncommon line\r\n",
+    }
+    reduce_response(response)
+    captured = capsys.readouterr()
+
+    # shared line should be prefixed with collapsed rank range
+    assert "0-2: common line" in captured.out
+    # unique lines should show only their rank
+    assert "  0: unique to 0" in captured.out
+    assert "  1: unique to 1" in captured.out
+    # header line is skipped
+    assert "header" not in captured.out
+
+
+def test_reduce_response_single_rank(capsys) -> None:
+    response = {
+        3: "header\r\nonly line\r\n",
+    }
+    reduce_response(response)
+    captured = capsys.readouterr()
+
+    assert "3: only line" in captured.out
+
+
 def test_strip_functions() -> None:
     text = "bt\r\n\x1b[?2004l\r#0  \x1b[33msimple\x1b[m () at \x1b[32msimple-mpi.f90\x1b[m:1\r\n\x1b[?2004h"
     text = strip_bracketted_paste(text)

From 5bac4de3be62d5828180b225b206d63d9992f566 Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Wed, 27 May 2026 15:16:55 +0100
Subject: [PATCH 4/9] feat: switch default back to pretty print and rename
 options

---
 src/mdb/mdb_shell.py            | 19 ++++---
 tests/output/answer-gdb.stdout  | 61 ++++++++++++++-------
 tests/output/answer-lldb.stdout | 94 ++++++++++++++++++++++-----------
 3 files changed, 115 insertions(+), 59 deletions(-)

diff --git a/src/mdb/mdb_shell.py b/src/mdb/mdb_shell.py
index c7393c1..94230d4 100644
--- a/src/mdb/mdb_shell.py
+++ b/src/mdb/mdb_shell.py
@@ -56,7 +56,7 @@ def __init__(self, shell_opts: ShellOpts, client: Client) -> None:
         self.exchange_select = parse_ranks(self.exchange_select_str)
         self.select_str = self.exchange_select_str
         self.select = self.exchange_select
-        self.output_mode = "reduce"  # 'pretty' or 'reduce'
+        self.output_mode = "separate"  # 'separate' or 'combined'
         backend_name = shell_opts["backend_name"].lower()
         if backend_name in backends:
             self.backend = backends[backend_name]()
@@ -216,7 +216,7 @@ def ask_remain_calm(signame: str) -> None:
 
         if command_response.msg_type == "exchange_command_response":
             response = sort_debug_response(command_response.data["results"])
-            if self.output_mode == "reduce":
+            if self.output_mode == "combined":
                 reduce_response(response)
             else:
                 pretty_print_response(response)
@@ -261,10 +261,13 @@ def do_set(self, line: str) -> None:
         Set mdb options.
 
         Example:
-        Switch output format between pretty-printed and reduced (deduplicated) mode:
+        Switch output format between separate and combined mode:
 
-            (mdb) set output pretty
-            (mdb) set output reduce
+            (mdb) set output combined
+            (mdb) set output separate
+
+        - separate shows all output for each rank separate by ***'s
+        - combined reduces common output across the ranks
 
         Show current settings:
 
@@ -276,15 +279,15 @@ def do_set(self, line: str) -> None:
 
         parts = line.split()
         if len(parts) < 2:
-            print("Usage: set output [pretty|reduce]")
+            print("Usage: set output [separate|combined]")
             return
 
         if parts[0].lower() == "output":
             mode = parts[1].lower()
-            if mode in ("pretty", "reduce"):
+            if mode in ("separate", "combined"):
                 self.output_mode = mode
             else:
-                print(f"Error: unknown output mode '{mode}'. Use 'pretty' or 'reduce'.")
+                print(f"Error: unknown output mode '{mode}'. Use 'separate' or 'combined'.")
         else:
             print(f"Error: unknown option '{parts[0]}'. Use 'output'.")
 
diff --git a/tests/output/answer-gdb.stdout b/tests/output/answer-gdb.stdout
index e6e9cb1..22a9a2f 100644
--- a/tests/output/answer-gdb.stdout
+++ b/tests/output/answer-gdb.stdout
@@ -1,18 +1,32 @@
 hello
-0-1: cmdline = simple-mpi.exe
-0-1: cwd = [mdb root]
-0-1: exe = simple-mpi.exe
-0-1: Breakpoint 2 at [hex address]: file simple-mpi.f90, line 15.
-0-1: Breakpoint 3 at [hex address]: file simple-mpi.f90, line 17.
-0-1: Continuing.
-0-1:
-0-1: Thread 1 "simple-mpi.exe" hit Breakpoint 2, simple () at simple-mpi.f90:15
-0-1: 15  var = 10.*process_rank
+0: cmdline = simple-mpi.exe
+0: cwd = [mdb root]
+0: exe = simple-mpi.exe
+************************************************************************
+1: cmdline = simple-mpi.exe
+1: cwd = [mdb root]
+1: exe = simple-mpi.exe
+0: Breakpoint 2 at [hex address]: file simple-mpi.f90, line 15.
+************************************************************************
+1: Breakpoint 2 at [hex address]: file simple-mpi.f90, line 15.
+0: Breakpoint 3 at [hex address]: file simple-mpi.f90, line 17.
+************************************************************************
+1: Breakpoint 3 at [hex address]: file simple-mpi.f90, line 17.
+0: Continuing.
+0:
+0: Thread 1 "simple-mpi.exe" hit Breakpoint 2, simple () at simple-mpi.f90:15
+0: 15  var = 10.*process_rank
+************************************************************************
+1: Continuing.
+1:
+1: Thread 1 "simple-mpi.exe" hit Breakpoint 2, simple () at simple-mpi.f90:15
+1: 15  var = 10.*process_rank
 0: Continuing.
 0:
 0: Thread 1 "simple-mpi.exe" hit Breakpoint 3, simple () at simple-mpi.f90:17
 0: 17  if (process_rank == 0) then
 0: #0  simple () at simple-mpi.f90:17
+************************************************************************
 1: #0  simple () at simple-mpi.f90:15
 unrecognized command [made-up-command]. Type help to find out list of possible commands.
 Error: user specified option [select] must be subset of available ranks (check mdb launch command).
@@ -22,15 +36,22 @@ select = [10] but available ranks are [0-1].
 1: Thread 1 "simple-mpi.exe" hit Breakpoint 3, simple () at simple-mpi.f90:17
 1: 17  if (process_rank == 0) then
 File [deliberately-missing-file.mdb] not found. Please check the file exists and try again.
-0-1: 25
-0-1: Continuing.
-  0:            1 s...
-  0:            2 s...
-  0:            3 s...
-0-1:  in level 1
-0-1:  in level 2
-  0:  internal process:            0 of            2
-  0:  var =    0.00000000
-  1:  internal process:            1 of            2
-  1:  var =    10.0000000
+0: 25
+************************************************************************
+1: 25
+0: Continuing.
+0:            1 s...
+0:            2 s...
+0:            3 s...
+0:  in level 1
+0:  in level 2
+0:  internal process:            0 of            2
+0:  var =    0.00000000
+************************************************************************
+1: Continuing.
+1:  in level 1
+1:  in level 2
+1:  internal process:            1 of            2
+1:  var =    10.0000000
+************************************************************************
 exiting mdb...
\ No newline at end of file
diff --git a/tests/output/answer-lldb.stdout b/tests/output/answer-lldb.stdout
index 82b0433..292e036 100644
--- a/tests/output/answer-lldb.stdout
+++ b/tests/output/answer-lldb.stdout
@@ -1,25 +1,50 @@
 hello
-0-1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 1.1
-0-1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:24:7
-0-1:    21    int process_rank, size_of_cluster;
-0-1:    22    float var;
-0-1:    23
-0-1: -> 24    var = 0.;
-0-1:           ^
-0-1:    25
-0-1:    26    MPI_Init(NULL, NULL);
-0-1:    27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
-0-1: Breakpoint 2: where = simple-mpi-cpp.exe`main + 95 at simple-mpi-cpp.cpp:30:12, address = [hex address]
-0-1: Breakpoint 3: where = simple-mpi-cpp.exe`main + 127 at simple-mpi-cpp.cpp:32:20, address = [hex address]
-0-1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
-0-1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
-0-1:    27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
-0-1:    28    MPI_Comm_rank(MPI_COMM_WORLD, &process_rank);
-0-1:    29
-0-1: -> 30    var = 10.*process_rank;
-0-1:                ^
-0-1:    31
-0-1:    32    if (process_rank == 0){
+0: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 1.1
+0:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:24:7
+0:    21    int process_rank, size_of_cluster;
+0:    22    float var;
+0:    23
+0: -> 24    var = 0.;
+0:           ^
+0:    25
+0:    26    MPI_Init(NULL, NULL);
+0:    27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
+************************************************************************
+1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 1.1
+1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:24:7
+1:    21    int process_rank, size_of_cluster;
+1:    22    float var;
+1:    23
+1: -> 24    var = 0.;
+1:           ^
+1:    25
+1:    26    MPI_Init(NULL, NULL);
+1:    27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
+0: Breakpoint 2: where = simple-mpi-cpp.exe`main + 95 at simple-mpi-cpp.cpp:30:12, address = [hex address]
+************************************************************************
+1: Breakpoint 2: where = simple-mpi-cpp.exe`main + 95 at simple-mpi-cpp.cpp:30:12, address = [hex address]
+0: Breakpoint 3: where = simple-mpi-cpp.exe`main + 127 at simple-mpi-cpp.cpp:32:20, address = [hex address]
+************************************************************************
+1: Breakpoint 3: where = simple-mpi-cpp.exe`main + 127 at simple-mpi-cpp.cpp:32:20, address = [hex address]
+0: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
+0:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
+0:    27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
+0:    28    MPI_Comm_rank(MPI_COMM_WORLD, &process_rank);
+0:    29
+0: -> 30    var = 10.*process_rank;
+0:                ^
+0:    31
+0:    32    if (process_rank == 0){
+************************************************************************
+1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
+1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
+1:    27    MPI_Comm_size(MPI_COMM_WORLD, &size_of_cluster);
+1:    28    MPI_Comm_rank(MPI_COMM_WORLD, &process_rank);
+1:    29
+1: -> 30    var = 10.*process_rank;
+1:                ^
+1:    31
+1:    32    if (process_rank == 0){
 0: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 3.1
 0:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:32:20
 0:    29
@@ -31,6 +56,7 @@ hello
 0:    35      for (int i = 0; i < 3; ++i) {
 0: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 3.1
 0:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:32:20
+************************************************************************
 1: * thread #1, name = 'simple-mpi-cpp.', stop reason = breakpoint 2.1
 1:     frame #0: [hex address] simple-mpi-cpp.exe`main at simple-mpi-cpp.cpp:30:12
 unrecognized command [made-up-command]. Type help to find out list of possible commands.
@@ -44,14 +70,20 @@ unrecognized command [made-up-command]. Type help to find out list of possible c
 1:    34
 1:    35      for (int i = 0; i < 3; ++i) {
 File [deliberately-missing-file.mdb] not found. Please check the file exists and try again.
-0-1: (int) 25
-  0: 0 s...
-  0: 1 s...
-  0: 2 s...
-0-1: in level 1
-0-1: in level 2
-  0: internal process: 0 of 2
-  0: var = 0
-  1: internal process: 1 of 2
-  1: var = 10
+0: (int) 25
+************************************************************************
+1: (int) 25
+0: 0 s...
+0: 1 s...
+0: 2 s...
+0: in level 1
+0: in level 2
+0: internal process: 0 of 2
+0: var = 0
+************************************************************************
+1: in level 1
+1: in level 2
+1: internal process: 1 of 2
+1: var = 10
+************************************************************************
 exiting mdb...
\ No newline at end of file

From cc8c5fd7ffdc9972864ae416d2bf9cb70c05d9ab Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Wed, 27 May 2026 15:28:13 +0100
Subject: [PATCH 5/9] docs: add tutorial for `set output` command

---
 docs/source/changing-output.rst | 157 ++++++++++++++++++++++++++++++++
 docs/source/index.rst           |   1 +
 2 files changed, 158 insertions(+)
 create mode 100644 docs/source/changing-output.rst

diff --git a/docs/source/changing-output.rst b/docs/source/changing-output.rst
new file mode 100644
index 0000000..dcbfab2
--- /dev/null
+++ b/docs/source/changing-output.rst
@@ -0,0 +1,157 @@
+.. Copyright 2023-2026 Tom Meltzer. See the top-level COPYRIGHT file for
+   details.
+
+.. _changing_output:
+
+Changing the Output Mode
+========================
+
+When debugging across multiple ranks, ``mdb`` can produce a large amount of output. By default,
+each rank's output is displayed independently, separated by divider lines. This is called *separate*
+mode and is the default behaviour.
+
+When the output from all ranks is identical, this can be redundant. The *combined* output mode
+reduces this verbosity by merging common lines across ranks into a single block, prefixing them
+with a combined rank range.
+
+This tutorial demonstrates the difference between the two modes using the ``set output`` command.
+
+The Example Program
+-------------------
+
+We will use the ``simple-mpi.exe`` binary from the ``examples/`` directory (see :ref:`quick_start`
+for details on compiling it).
+
+Launching the Debug Target
+--------------------------
+
+First, launch the program with two processes::
+
+    $ mdb launch -n 2 -t ./simple-mpi.exe
+
+This starts the debug server and waits for an ``mdb attach`` connection.
+
+Separate Output Mode (Default)
+------------------------------
+
+In separate mode, each rank's output is printed independently. The output from each rank is
+prefixed with its rank ID (e.g., ``0:`` or ``1:``) and blocks for different ranks are separated by
+a line of asterisks (``****``).
+
+Create a script file ``script-separate.mdb``::
+
+    set output separate
+    broadcast start
+    info proc
+    break 15
+    continue
+    list
+    continue
+    quit
+    quit
+
+Run it with::
+
+    $ mdb attach -x script-separate.mdb > separate.out
+
+Here is a shortened excerpt of the output from the ``info proc`` and ``list`` commands:
+
+**``info proc`` in separate mode:**
+
+.. code-block:: console
+
+   0: process 44900
+   0: cmdline = '/home/melt/sync/cambridge/projects/side/mdb/examples/simple-mpi.exe'
+   0: cwd = '/home/melt/sync/cambridge/projects/side/mdb'
+   0: exe = '/home/melt/sync/cambridge/projects/side/mdb/examples/simple-mpi.exe'
+   ************************************************************************
+   1: process 44903
+   1: cmdline = '/home/melt/sync/cambridge/projects/side/mdb/examples/simple-mpi.exe'
+   1: cwd = '/home/melt/sync/cambridge/projects/side/mdb'
+   1: exe = '/home/melt/sync/cambridge/projects/side/mdb/examples/simple-mpi.exe'
+
+Each rank's output appears in its own block, prefixed with just the rank number, separated by
+``****`` dividers.
+
+**``list`` in separate mode:**
+
+.. code-block:: console
+
+   0: 10
+   0: 11   call mpi_init(ierror)
+   0: 12   call mpi_comm_size(mpi_comm_world, size_of_cluster, ierror)
+   0: 13   call mpi_comm_rank(mpi_comm_world, process_rank, ierror)
+   0: 14
+   0: 15   var = 10.*process_rank
+   0: 16
+   0: 17   if (process_rank == 0) then
+   0: 18     print *, 'process 0 sleeping for 3s...'
+   0: 19     do i = 1, 3
+   ************************************************************************
+   1: 10
+   1: 11   call mpi_init(ierror)
+   1: 12   call mpi_comm_size(mpi_comm_world, size_of_cluster, ierror)
+   1: 13   call mpi_comm_rank(mpi_comm_world, process_rank, ierror)
+   1: 14
+   1: 15   var = 10.*process_rank
+   1: 16
+   1: 17   if (process_rank == 0) then
+   1: 18     print *, 'process 0 sleeping for 3s...'
+   1: 19     do i = 1, 3
+
+Since the source code is identical across ranks, the ``list`` output is duplicated for each rank.
+
+Combined Output Mode
+--------------------
+
+In combined mode, lines that are identical across all ranks are merged and prefixed with a combined
+rank range (e.g., ``0-1:``). Lines that differ between ranks are still shown per-rank with a single
+rank prefix (e.g., ``  0:``). No ``****`` dividers are used.
+
+Create a script file ``script-combined.mdb``::
+
+    set output combined
+    broadcast start
+    info proc
+    break 15
+    continue
+    list
+    continue
+    quit
+    quit
+
+Run it with::
+
+    $ mdb attach -x script-combined.mdb > combined.out
+
+**``info proc`` in combined mode:**
+
+.. code-block:: console
+
+      0: process 45004
+   0-1: cmdline = '/home/melt/sync/cambridge/projects/side/mdb/examples/simple-mpi.exe'
+   0-1: cwd = '/home/melt/sync/cambridge/projects/side/mdb'
+   0-1: exe = '/home/melt/sync/cambridge/projects/side/mdb/examples/simple-mpi.exe'
+      1: process 45005
+
+Notice how the three identical lines (``cmdline``, ``cwd``, ``exe``) are merged under a single
+``0-1:`` prefix. The ``process`` line differs between ranks (different PIDs) so it is shown
+individually for each rank.
+
+**``list`` in combined mode:**
+
+.. code-block:: console
+
+   0-1: 10
+   0-1: 11   call mpi_init(ierror)
+   0-1: 12   call mpi_comm_size(mpi_comm_world, size_of_cluster, ierror)
+   0-1: 13   call mpi_comm_rank(mpi_comm_world, process_rank, ierror)
+   0-1: 14
+   0-1: 15   var = 10.*process_rank
+   0-1: 16
+   0-1: 17   if (process_rank == 0) then
+   0-1: 18     print *, 'process 0 sleeping for 3s...'
+   0-1: 19     do i = 1, 3
+
+Since all ranks share the same source code, every line is identical and merged into a single
+compact block. This avoids the duplication seen in separate mode.
diff --git a/docs/source/index.rst b/docs/source/index.rst
index eccdf0e..93db5f0 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -19,6 +19,7 @@ serial debugger backends e.g.,  `gdb <https://sourceware.org/gdb>`_ and `lldb
 
    Installation <installation>
    Quick Start <quick-start>
+   Changing the Output Mode <changing-output>
    Debugging AMD GPU Kernels <gpu-amd>
 
 .. toctree::

From 9942ea59715de8d846c3c270b29b9db3c521a294 Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Wed, 27 May 2026 15:31:26 +0100
Subject: [PATCH 6/9] chore: bump version for v1.0.7 release

---
 pyproject.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index be47452..3dce575 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "mdb_debugger"
-version = "1.0.6"
+version = "1.0.7"
 dependencies = [
     "click==8.1.7",
     "matplotlib==3.8.3",

From 69a9bfeb40f5cabb8f09e2a13f83e1e1f6162f2d Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Wed, 27 May 2026 16:05:43 +0100
Subject: [PATCH 7/9] chore: black format fix

---
 src/mdb/mdb_shell.py | 4 +++-
 src/mdb/utils.py     | 4 +---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/mdb/mdb_shell.py b/src/mdb/mdb_shell.py
index 94230d4..ff26571 100644
--- a/src/mdb/mdb_shell.py
+++ b/src/mdb/mdb_shell.py
@@ -287,7 +287,9 @@ def do_set(self, line: str) -> None:
             if mode in ("separate", "combined"):
                 self.output_mode = mode
             else:
-                print(f"Error: unknown output mode '{mode}'. Use 'separate' or 'combined'.")
+                print(
+                    f"Error: unknown output mode '{mode}'. Use 'separate' or 'combined'."
+                )
         else:
             print(f"Error: unknown option '{parts[0]}'. Use 'output'.")
 
diff --git a/src/mdb/utils.py b/src/mdb/utils.py
index 5dac63b..de9f34f 100644
--- a/src/mdb/utils.py
+++ b/src/mdb/utils.py
@@ -120,9 +120,7 @@ def extract_float(line: str, backend: "DebugBackend") -> float:
 
 
 def prepend_ranks(rank: int, result: str) -> str:
-    return "".join(
-        [f"{rank}: " + line + "\r\n" for line in result.split("\r\n")[1:-1]]
-    )
+    return "".join([f"{rank}: " + line + "\r\n" for line in result.split("\r\n")[1:-1]])
 
 
 def strip_bracketted_paste(text: str) -> str:

From ba13c4cf9ce5f6728bae7962c6b1cf2fbe749817 Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Wed, 27 May 2026 16:07:31 +0100
Subject: [PATCH 8/9] chore: fix typo in docs

---
 docs/source/changing-output.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/source/changing-output.rst b/docs/source/changing-output.rst
index dcbfab2..3a69b76 100644
--- a/docs/source/changing-output.rst
+++ b/docs/source/changing-output.rst
@@ -128,11 +128,11 @@ Run it with::
 
 .. code-block:: console
 
-      0: process 45004
+     0: process 45004
    0-1: cmdline = '/home/melt/sync/cambridge/projects/side/mdb/examples/simple-mpi.exe'
    0-1: cwd = '/home/melt/sync/cambridge/projects/side/mdb'
    0-1: exe = '/home/melt/sync/cambridge/projects/side/mdb/examples/simple-mpi.exe'
-      1: process 45005
+     1: process 45005
 
 Notice how the three identical lines (``cmdline``, ``cwd``, ``exe``) are merged under a single
 ``0-1:`` prefix. The ``process`` line differs between ranks (different PIDs) so it is shown

From 70f21feb6ffeb99d5a4f712f2ba5ca32c653b6b5 Mon Sep 17 00:00:00 2001
From: melt <thomas.meltzer1@gmail.com>
Date: Wed, 27 May 2026 16:11:56 +0100
Subject: [PATCH 9/9] chore: fix mypy errors

---
 tests/test_utils.py | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tests/test_utils.py b/tests/test_utils.py
index a840e00..a9401f0 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -1,6 +1,8 @@
 # Copyright 2023-2026 Tom Meltzer. See the top-level COPYRIGHT file for
 # details.
 
+import pytest
+
 from mdb.utils import (
     collapse_ranges,
     parse_ranks,
@@ -51,7 +53,7 @@ def test_collapse_ranges() -> None:
     assert collapse_ranges([1, 2, 5, 6, 7, 10]) == "1-2,5-7,10"
 
 
-def test_pretty_print_response(capsys) -> None:
+def test_pretty_print_response(capsys: pytest.CaptureFixture[str]) -> None:
     response = {
         0: "command ran\r\nline 1\r\nline 2\r\n",
         1: "command ran\r\nline 3\r\n",
@@ -67,7 +69,7 @@ def test_pretty_print_response(capsys) -> None:
     assert "command ran" not in captured.out
 
 
-def test_reduce_response(capsys) -> None:
+def test_reduce_response(capsys: pytest.CaptureFixture[str]) -> None:
     response = {
         0: "header\r\ncommon line\r\nunique to 0\r\n",
         1: "header\r\ncommon line\r\nunique to 1\r\n",
@@ -85,7 +87,7 @@ def test_reduce_response(capsys) -> None:
     assert "header" not in captured.out
 
 
-def test_reduce_response_single_rank(capsys) -> None:
+def test_reduce_response_single_rank(capsys: pytest.CaptureFixture[str]) -> None:
     response = {
         3: "header\r\nonly line\r\n",
     }