{"record":{"id":"12e60f6723eff9e1","repo":"GoogleContainerTools/skaffold","slug":"the-length-of-stdout-should-be-greater-than-0-when","errorCode":null,"errorMessage":"the length of stdout should be greater than 0 when using render post hook with change","messagePattern":"the length of stdout should be greater than 0 when using render post hook with change","errorType":"validation","errorClass":null,"httpStatus":null,"severity":"error","filePath":"pkg/skaffold/hooks/render.go","lineNumber":99,"sourceCode":"\t}\n\tenv := r.getEnv()\n\tfor _, h := range r.PostHooks {\n\t\tif h.HostHook != nil {\n\t\t\thook := hostHook{latest.HostHook{\n\t\t\t\tCommand: h.HostHook.Command,\n\t\t\t\tOS:      h.HostHook.OS,\n\t\t\t\tDir:     h.HostHook.Dir,\n\t\t\t}, env}\n\t\t\tvar b bytes.Buffer\n\t\t\tif h.HostHook.WithChange {\n\t\t\t\tif err := hook.run(ctx, updated.Reader(), &b); err != nil {\n\t\t\t\t\tif errors.Is(err, &Skip{}) {\n\t\t\t\t\t\tcontinue\n\t\t\t\t\t}\n\t\t\t\t\treturn manifest.ManifestList{}, err\n\t\t\t\t}\n\t\t\t\tif b.Len() == 0 {\n\t\t\t\t\treturn manifest.ManifestList{}, fmt.Errorf(\"the length of stdout should be greater than 0 when using render post hook with change\")\n\t\t\t\t}\n\t\t\t\tupdated, err = manifest.Load(&b)\n\t\t\t\tif err != nil {\n\t\t\t\t\treturn manifest.ManifestList{}, fmt.Errorf(\"failed to load manifest\")\n\t\t\t\t}\n\t\t\t} else {\n\t\t\t\tif err := hook.run(ctx, updated.Reader(), logWriter); err != nil && !errors.Is(err, &Skip{}) {\n\t\t\t\t\treturn manifest.ManifestList{}, err\n\t\t\t\t}\n\t\t\t}\n\t\t}\n\t}\n\tif len(r.PostHooks) > 0 {\n\t\toutput.Default.Fprintln(logWriter, fmt.Sprintf(\"Completed %s hooks\", phases.PostRender))\n\t}\n\treturn updated, nil\n}\n","sourceCodeStart":81,"sourceCodeEnd":117,"githubUrl":"https://github.com/GoogleContainerTools/skaffold/blob/a1189de023efc32d4b8e11f395acc678aa555011/pkg/skaffold/hooks/render.go#L81-L117","documentation":"RunPostHooks in skaffold's render hook pipeline runs a user-defined post-render hook that may modify the rendered manifests. After such a 'change' hook runs, skaffold reloads the manifest from the hook's captured stdout buffer; if the buffer is empty (the hook printed nothing), skaffold cannot reload anything and fails fast with this explicit message rather than silently treating the manifests as deleted/empty.","triggerScenarios":"A render post-hook configured with OS command + `when: change` runs successfully (exit 0, no Skip) but writes nothing to stdout, so b.Len() == 0 when manifest.Load(&b) is attempted.","commonSituations":"Hook command redirects output to a file instead of stdout; hook echoes to stderr; hook silently no-ops because its condition didn't match (e.g. no matching files); a YAML-processing tool (yq, kustomize) invoked with wrong flags that produce empty output; writing a script that logs progress to stdout and pipes the manifest elsewhere.","solutions":["Make the hook command print the full modified manifest JSON/YAML to stdout (e.g. `yq eval '...'` without -i; use `yq eval -i` only for file mode, not stdout mode)","Fix redirection mistakes: remove `> file`, `2>&1 >/dev/null`, or tee-to-file patterns that consume stdout","Verify the hook actually processes the input manifests rather than exiting early on a no-match condition"],"exampleFix":"// before (skaffold.yaml)\npostHooks:\n  host:\n    command: [\"sh\", \"-c\", \"cat manifests.yaml | yq e '.metadata.namespace = \\\"prod\\\"' -i\"]\n// after\npostHooks:\n  host:\n    command: [\"sh\", \"-c\", \"cat manifests.yaml | yq e '.metadata.namespace = \\\"prod\\\"' -\"]","handlingStrategy":"validation","validationCode":"// before relying on a change-type render post hook, verify it emits the manifest on stdout:\nout=$(sh -c \"$hook_command\" <<< \"$manifests\")\nif [ -z \"$out\" ]; then echo 'hook stdout is empty; fix the hook to print manifests' >&2; exit 1; fi","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Never redirect hook stdout to a file; print the transformed manifest to stdout","Send logs/diagnostics to stderr only","Test change hooks locally by piping a sample manifest and checking output is non-empty and parseable"],"tags":["render","hooks","manifests","skaffold"],"backgroundTag":"empty-hook-stdout","analyzedSha":"a1189de023efc32d4b8e11f395acc678aa555011","analyzedAt":"2026-09-05T12:09:27.064Z","contentChangedAt":"2026-09-05T12:09:27.064Z","schemaVersion":2},"datasetVersion":"2026-09-12T17:17:11.597Z"}