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Pull request overview
This PR adds a mechanism for hooks to pass data back to Kamal by writing KEY=VALUE pairs to a file specified by the $KAMAL_OUTPUT environment variable. Hook outputs accumulate across the deploy lifecycle and are made available to subsequent hooks through environment variables, with a proper precedence order ensuring secrets and built-in tags cannot be overridden.
Changes:
- New
Kamal::HookOutputclass manages temporary file lifecycle and parses dotenv-formatted output - Hook outputs accumulate in
Commander#hook_outputsand are passed to subsequent hooks viaCommands::Hook#env - Special
KAMAL_MESSAGEkey is displayed to users after hook completion
Reviewed changes
Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| lib/kamal/hook_output.rb | New class for managing hook output tempfile and parsing dotenv format |
| lib/kamal/cli/base.rb | Creates HookOutput, passes path to hooks, parses output, displays messages, ensures cleanup |
| lib/kamal/commander.rb | Adds hook_outputs accumulator and merge_hook_output method |
| lib/kamal/commands/hook.rb | Merges accumulated hook outputs into hook environment with correct precedence (secrets > tags > hook_outputs) |
| lib/kamal/cli/templates/sample_hooks/*.sample | Documents KAMAL_OUTPUT environment variable availability |
| test/hook_output_test.rb | Comprehensive unit tests for HookOutput parsing and cleanup |
| test/commands/hook_test.rb | Tests for hook environment with hook_outputs and precedence rules |
| test/commander_test.rb | Tests for hook_outputs accumulation behavior |
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Hooks are fire-and-forget today: exit code is the only feedback channel. This adds a file-based output channel so hooks can set variables that Kamal reads back. Before each hook, Kamal creates a tempfile and passes its path as KAMAL_OUTPUT. The hook writes dotenv-format KEY=VALUE lines. Kamal parses them after the hook exits and accumulates them on Commander, merging into the env for subsequent hooks. A pre-deploy hook that writes DEPLOY_ID=123 makes $DEPLOY_ID available to post-deploy. KAMAL_MESSAGE is special: if present, Kamal prints it regardless of verbosity settings, giving hooks a dedicated user-facing output channel separate from stdout logging. Backward-compatible: hooks that don't write to KAMAL_OUTPUT behave identically to today.
Summary
KEY=VALUElines (dotenv format) to the file at$KAMAL_OUTPUTKAMAL_MESSAGEis printed to the user after the hook completespre-deployhook that writesDEPLOY_ID=123makes$DEPLOY_IDavailable topost-deploy$KAMAL_OUTPUTbehave identically to beforeFiles
lib/kamal/hook_output.rb— new: tempfile lifecycle + dotenv parsinglib/kamal/cli/base.rb—run_hookcreates HookOutput, passesKAMAL_OUTPUT, parses output, printsKAMAL_MESSAGE, cleans up inensurelib/kamal/commander.rb—hook_outputsaccumulator,merge_hook_outputlib/kamal/commands/hook.rb— merge accumulated hook outputs into hook env with correct precedenceKAMAL_OUTPUTTest plan
test/hook_output_test.rb— 7 tests: parse, cleanup, empty file, quoted values, path accesstest/commander_test.rb— 3 new tests: starts empty, accumulates, overwritestest/commands/hook_test.rb— 3 new tests: env with hook_outputs, cannot override tags, cannot override secrets