On Windows + Git Bash, the SessionStart hook prints a confusing
diagnostic at every startup ("printf: write error: Permission denied")
when Claude Code closes the hook's stdout pipe before the printf has
finished writing. The hook still runs to completion and context still
gets injected, but the diagnostic surfaces every session because
Git Bash's printf reports EPIPE as "Permission denied" (not "Broken
pipe" like Linux) and our `set -euo pipefail` lets that error escape.
Piping each printf through `cat` makes the external cat process the
recipient of any SIGPIPE / EPIPE. cat's failure does not propagate to
the parent bash under pipefail because cat is the last command in the
pipeline and exits cleanly when the pipe stays open long enough to
hold the data. On macOS/Linux the cat passthrough is transparent (no
behavior change, no measurable cost).
Verified:
- Existing tests/hooks/test-session-start.sh: 7/7 pass on macOS
- Manual run on Windows 11 + Git Bash 5.2 + Node 22 produces valid JSON,
clean stderr, and exit 0
- JSON output is byte-identical to the unpatched hook
Reported by @silvertakana in #1612, attribution preserved in the
Co-authored-by trailer below — this is the same fix shape the original
PR proposed.
Co-authored-by: silvertakana <silvertakana@users.noreply.github.com>
Closes#1612.
Copilot CLI v1.0.11 reads `additionalContext` from sessionStart hook
output, but the session-start script only emits the Claude Code-specific
nested format. Add COPILOT_CLI env var detection so Copilot CLI gets the
SDK-standard top-level `additionalContext` while Claude Code continues
getting `hookSpecificOutput`.
Based on PR #910 by @culinablaz.
Add hooks/hooks-cursor.json with Cursor's camelCase format (sessionStart,
version: 1) and update .cursor-plugin/plugin.json to reference it. Uses
${CURSOR_PLUGIN_ROOT} and run-hook.cmd for cross-platform support.
Fix session-start platform detection: check CURSOR_PLUGIN_ROOT first
(Cursor may also set CLAUDE_PLUGIN_ROOT), ensuring correct output format
for each platform.
Based on PR #709 with fixes for: wrong filename (.sh extension), missing
Windows support, fragile relative paths, and incorrect platform detection.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Bash 5.3 has a regression where heredoc variable expansion blocks when
content exceeds ~512 bytes. The session_context variable is ~4,500 bytes,
causing the SessionStart hook to hang indefinitely on macOS with Homebrew
bash 5.3+. Replace cat <<EOF with printf.
Tested on Linux (bash 5.2) and Windows (Git Bash 5.2). The hang only
affects 5.3+ but printf works correctly on all versions.
Based on #572, closes#572. Fixes#571.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Replace ${BASH_SOURCE[0]:-$0} with $0 in hooks/session-start and the
polyglot-hooks docs example. BASH_SOURCE uses bash array syntax that
causes 'Bad substitution' on systems where /bin/sh is dash (Ubuntu).
Since session-start is always executed (never sourced), $0 and
BASH_SOURCE give the same result. Tested on Linux (bash + dash) and
Windows (Git Bash via CMD and direct).
Based on #553, closes#553.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Claude Code reads both additional_context and hookSpecificOutput without
deduplication, causing double injection. Detect platform via
CLAUDE_PLUGIN_ROOT and emit only the appropriate field.
Co-authored-by: mvanhorn <mvanhorn@users.noreply.github.com>
Claude Code spawns hook commands with shell:true + windowsHide:true,
but on Windows the execution chain cmd.exe -> bash.exe causes Git
Bash (MSYS2) to allocate its own console window, bypassing the hide
flag. This creates visible terminal windows that steal focus on every
SessionStart event (startup, resume, clear, compact).
The fix:
- Rename session-start.sh to session-start (no extension) so Claude
Code's .sh auto-detection regex doesn't fire and prepend "bash"
- Restore run-hook.cmd polyglot wrapper to control bash invocation
on Windows (tries known Git Bash paths, then PATH, then exits
silently if no bash found)
- On Unix, the polyglot's shell portion runs the script directly
This avoids Claude Code's broken .sh auto-prepend, gives us control
over how bash is invoked on Windows, and gracefully handles missing
bash instead of erroring.
Addresses: #440, #414, #354, #417, #293
Upstream: anthropics/claude-code#14828
