Adds new version of help50

[dmalan]

To be squashed when merging.

This new version is implemented in Bash (instead of Python) as follows, wherein usage is inspired by systemctl, even though it doesn't run as a daemon but, rather, per login shell. It runs locally and automatically now, without any server. In a codespace, failures that no local helper recognizes can additionally be handed to the CS50 Duck (see Related repositories below); in plain cs50/cli, help is printed in the terminal.

• help50 start sets $HELP50 to /tmp/help50.$PPID (the PID of the shell in which the command was run) and launches script, which logs standard I/O to that file. Started automatically by /etc/profile.d/cli.sh for interactive shells that have a terminal, if enabled; never for non-interactive shells like bash --login -c, where script would otherwise block.
• help50 stop sends SIGTERM to script, which returns the user to the outer, unhelped shell.
• help50 status checks for $HELP50, which is set only when help50 is started for a shell.
• help50 disable writes /tmp/help50.lock.
• help50 enable deletes /tmp/help50.lock.
• help50 is-enabled checks for /tmp/help50.lock, and for $HELP50_DISABLED in the environment. The latter is a kill switch: any value other than 0, false, no, or off disables help50 at login and is reported as such, so that, delivered as a Codespaces secret, help50 can be turned off fleet-wide at each student's next codespace start without rebuilding an image.
• help50 COMMAND [ARGS...] runs COMMAND as though it had been typed directly, with the same exit status, so that students who remember the old help50 make foo get exactly the behavior of make foo. Within a help50 session this is a shell function that evals COMMAND in the shell itself, so aliases, functions, and cd behave as they would have; outside one, /opt/cs50/bin/help50 execs it. Bare help50 prints usage explaining that help is now automatic.

---

• /etc/profile.d/help50.sh is a config that that's only sourced when $HELP50 is set.
  • It sets $PROMPT_COMMAND to _help50, which is a Bash function implemented therein that, if the most recent command exited with non-0 status (per $?, ignoring ctl-c and ctl-z), reads $HELP50, strips ANSI and control characters (via ansi2txt and col), and drops everything through the command line itself as echoed by the terminal (so that tab-completion listings, history recall, and redrawn prompts aren't mistaken for output). The read is bounded to the first 64K and last 1M of the file, and long output is capped to its first 64 and last 1,024 lines with a marker in between, so the prompt's cost doesn't grow with how much a program printed before failing. What remains is passed as standard input, with the command's own words as arguments, to each executable in /opt/cs50/lib/help50/ (implemented in any language), each under a 5-second timeout.
  • If any of those echo output, it passes it to a _helpful function that, by default, displays it in yellow to help the user (and, for one prompt, aliases y, yes, n, and no to a reminder that the question was rhetorical, since yes and n are real programs).
  • If none of those echo output, it passes the failed command's output (its last 8K) and command line to _helpless OUTPUT CMD instead, which doesn't do anything in cs50/cli but is overridden in cs50/codespace to relay them to ddb50.
  • Else if the most recent command exited successfully, _helped is called, which doesn't do anything in cs50/cli but is overridden in cs50/codespace to indicate to the user that help is (no longer) available.
• /etc/profile.d/cli.sh starts help50 automatically, as above.
• /opt/cs50/lib/cli contains several helper functions (written in Bash) that our own wrappers and help50 use: _alert, _ansi, _find, _fold, _sure. The make, sqlite3, http-server, and valgrind wrappers now use them, and the make wrapper lets make itself report make foo.c so that the make helper can explain it.
• /opt/cs50/lib/help50/ contains helpers for bash (e.g., 1s, a capitalized command, check 50, ./foo.c, .\foo, a directory run as a command, code typed into the terminal), cd (e.g., cd.., or a directory that exists elsewhere in the workspace), clang (a file without main), make (e.g., make foo.c, or a target whose .c file is elsewhere), and python (e.g., a file shadowing cs50, re, or string, or a file that exists elsewhere). Each verifies its hypothesis against the filesystem before advising; "elsewhere" searches $WORKDIR.
• Dockerfile installs bsdextrautils (for col), colorized-logs (for ansi2txt), file, expect, and fzf, and no longer installs the Python help50 package.
• tests/smoke.sh (also make smoke) checks a built image under timeouts, and .github/workflows/main.yml runs it against each architecture's build before pushing to Docker Hub.

---

$ git fetch
$ git checkout help50
$ make build
$ make run

/mnt/ $ help50 start

/mnt/ $ ps f
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 bash --login
   24 pts/0    S      0:00 /bin/bash /opt/cs50/bin/help50 start
   26 pts/0    S+     0:00  \_ script --append --command bash --login ; exit 1 --flush --quiet --return /tmp/help50.1
   27 pts/1    Ss     0:00      \_ sh -c bash --login ; exit 1
   28 pts/1    S      0:00          \_ bash --login
  143 pts/1    R+     0:00              \_ ps f

/mnt/ $ help50 stop

Session terminated, killing shell... ...killed.

/mnt/ $ ps f
  PID TTY      STAT   TIME COMMAND
    1 pts/0    Ss     0:00 bash --login
  178 pts/0    R+     0:00 ps f

(In a codespace, script spawns bash -c rather than sh -c, per $SHELL, and the outermost shell is VS Code's bash --login -i.)

---

Related repositories

This PR is the foundation; the rest of the pipeline lives elsewhere. Everything below is merged to its integration branch unless noted.

Repository	Role	PRs
cs50/cli	Shell detection, helpers, help50 controller (this PR)	#244 bug fixes + smoke test, #245 ignore terminal echo before the command line, #246 keep the end of long output + pass the command line to _helpless, #247 help50 COMMAND passthrough, #248 bounded read, helper timeout, HELP50_DISABLED
cs50/codespace	Overrides _helpful/_helpless/_helped to relay to the help50 extension via command50; sets WORKDIR to the workspace; installs help50.vsix; Sysadmins terminal profile; smoke test	#196 integration, #197 clear a stale button after a quiet failure, #198 inline advice only, no button, #199 send the command line with the output (all on canary); #200 rollout to main
cs50/help50.vsix	The help50 button in the terminal's title bar; on click, hands the failed command's transcript to ddb50	#1 hardening + engine/deps, #2 button as text, #3 hide the button before dispatching
cs50/ddb50.vsix	The CS50 Duck; requestGptResponse posts the transcript to cs50.ai's /api/v1/help	#23 wait for the webview to be ready, #24 reset on hide, #25 fix the cold-start wait
cs50/cs50.vsix	command50, the shell-to-VS Code bridge (WebSocket) that the codespace overrides use	#58 Python 3.14 compatibility + VS Code process detection, #59 audit fixes
cs50/cs50.dev	Delivers the HELP50_DISABLED kill switch as a per-student Codespaces secret when set on the server	#212
cs50/cs50.ai, cs50/cs50.ai-config	/api/v1/help (added 2024-10-09) wraps the transcript in the help50_* prompts of configs/chat_cs50.yml	no changes needed
cs50/cs50.readthedocs.io	Documentation: cs50.readthedocs.io/help50	#184
cs50/harvard	Course pages: help50 make hello advice replaced with what students now see	#485 (2026/fall), #486 (2026/x)

Data flow in a codespace: failed command → _help50 → helpers → _helpless OUTPUT CMD → command50 help50.showButton ask "$ CMD\nOUTPUT" → help50.vsix shows the button → click → ddb50 requestGptResponse → POST https://cs50.ai/api/v1/help.

Progression

• 2024-01 to 2024-10 — Implemented, iterated, and marked ready for review (dmalan). cs50.ai's /api/v1/help and help50.vsix were created alongside (2024-10).
• 2026-09-20 — Merged main into help50.
• 2026-09-21 — Bug fixes found by testing and review, and a smoke test in CI (Fix help50 bugs and add smoke test #244); terminal echo no longer mistaken for output (Ignore terminal echo before the command line in typescripts #245). Codespace integration landed on canary (Add help50 integration codespace#196–Adds support for R, tidied Dockerfile #198) with help50.vsix#1–adds stdeb and its dependencies #2, ddb50.vsix#23–added server as reverse dependency #24, and cs50.vsix#58–installing gems in GEM_HOME #59, and was verified end to end in a canary codespace.
• 2026-09-22 — Long output keeps its tail and the duck receives the command line (Keep the end of long output, and pass the command line to _helpless #246, Send the command line along with the output to the duck codespace#199); help50 COMMAND passthrough (Run help50 COMMAND as though COMMAND were typed directly #247).
• 2026-09-29/30 — Safety pass: bounded typescript read, per-helper timeout, HELP50_DISABLED (Bound the prompt hook's cost, and add a kill switch #248); cold-start fixes in ddb50.vsix#25 and help50.vsix#3; kill switch delivery via cs50.dev#212. Codespace changes promoted to main (Help50 rollout codespace#200). Documentation: cs50.readthedocs.io#184, and course pages in cs50/harvard#485 and #486.

Rollout

1. Merge this PR, which publishes cs50/cli:latest.
2. Rebuild cs50/codespace (main, already merged via Help50 rollout codespace#200), which builds on it.
3. Students pick it up on their next codespace rebuild.

Escape hatches, should help50 misbehave: ctl-c interrupts the prompt hook; help50 stop for the current shell; help50 disable for a codespace's new shells; a student's own HELP50_DISABLED Codespaces secret; and, fleet-wide without a rebuild, HELP50_DISABLED=1 on cs50.dev (0 deletes the secret again). Root shells (the codespace's Sysadmins profile) never start help50.

[rongxin-liu]

All checks passed, still need 1 approving review by you @rongxin-liu . Looks like all checks passed.

Thanks for the reminder. How did you perform the test?