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[correctness][confirmed-defect][builtins/printf] printf hexadecimal zero padding exceeds the requested width

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
74/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
go
Domain
cli

Research direction

The bug is in the %#0...x branch at builtins/printf/printf.go:591, which passes the format straight to fmt.Sprintf, so the 0x prefix is counted outside the zero-padding width. Start there and run printf '%#08x\n' 31 to reproduce; Bash prints 0x00001f. Done when the output is 0x00001f and a scenario added under tests/scenarios/cmd/printf/width_precision/ passes.

Written by the indexing model from the issue text.

Description

Generated by the rshell behavior correctness scanner.

  • Contract: BEH-007
  • Classification: confirmed-defect
  • Impact: low
  • Target: builtins/printf
  • Scanned commit: 514d1cb8188fda6b1accca5955dfab3b0e8aa34a

For %#08x, the 0x prefix should be included in the eight-character width. Go formatting adds it outside the zero-padding width, producing ten characters.

Contract sources
  • [SHELL_FEATURES.md:42](https://github.com/datadog/rshell/blob/514d1cb8188fda6b1accca5955dfab3b0e8aa34a/SHELL_FEATURES.md#L42): Supported surface; Bash/GNU behavior applies where no intentional divergence is documented.
Implementation references
  • [builtins/printf/printf.go:591](https://github.com/datadog/rshell/blob/514d1cb8188fda6b1accca5955dfab3b0e8aa34a/builtins/printf/printf.go#L591): The %#0...x format is delegated directly to fmt.Sprintf, whose prefix-width behavior differs.

Fixture setup

Use a fresh empty working directory for each run. Build from /workspace/repo first. No fixture files are needed. Run the CLI and reference commands with that directory as cwd.

Reproducer

printf '%#08x\n' 31

Commands used:

  • GOENV_VERSION=1.26.3 timeout 300s go build -o /tmp/zz_correctness_scan_rshell ./cmd/rshell
  • /tmp/zz_correctness_scan_rshell --allow-all-commands --allowed-paths "$PWD" -c 'printf '"'"'%#08x\n'"'"' 31 '
  • LC_ALL=C.UTF-8 /usr/bin/bash --noprofile --norc -c 'printf '"'"'%#08x\n'"'"' 31 '
  • GOENV_VERSION=1.26.3 timeout 300s go test ./tests -run '^TestShellScenarios$/^.$/zz_correctness_scan_report_' -count=2 -v -timeout 300s
Expected

Exit code: 0

stdout:

0x00001f

stderr:
Actual

Exit code: 0

stdout:

0x0000001f

stderr:

Verification

  • Reproduction runs: 4
  • Reference: Two fresh CLI fixtures and two fresh scenario fixtures; exploratory runs excluded. Native Bash 5.2.21, GNU coreutils 9.4, grep 3.11, sed 4.9, LC_ALL=C.UTF-8. Docker comparison attempted but image pull returned HTTP 502.
  • Temporary test: tests/scenarios/zz_correctness_scan_report_printf_hex.yaml (removed after evidence capture)
  • Suggested regression-test location: tests/scenarios/cmd/printf/width_precision/

Fingerprint: 5d9d4ff2741d619577d03418cae78fd4c74a2f671c5efa61c3342282bfb1e617

Dominant language
Go
Stars
31
Forks
3
Avg merge
2d 9h
Merged PRs (30d)
14

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