uutils/coreutils

date: strftime ignores flags and widths on %N (nanoseconds)

Open

#11658 opened on Apr 5, 2026

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U - datefuzzinggood first issue

Description

Summary

GNU date honours strftime flags and widths on %N (nanoseconds). uutils ignores or mishandles them: %_3N should space-pad to width 3, and %-N should still emit the full 9-digit default, but uutils emits a single 0.

Found by a fuzz_date run.

Reproduction

$ LC_ALL=C TZ=UTC /usr/bin/date -d '@0' '+%_3N' | od -c | head -1
0000000   0                \n

$ LC_ALL=C TZ=UTC target/debug/coreutils date -d '@0' '+%_3N' | od -c | head -1
0000000   0  \n

$ LC_ALL=C TZ=UTC /usr/bin/date -d '@0' '+%-N'
000000000

$ LC_ALL=C TZ=UTC target/debug/coreutils date -d '@0' '+%-N'
0

Test

#[test]
fn test_date_strftime_n_width_and_flags() {
    new_ucmd!()
        .env("LC_ALL", "C")
        .env("TZ", "UTC")
        .arg("-d")
        .arg("@0")
        .arg("+%_3N")
        .succeeds()
        .stdout_is("0  \n");

    new_ucmd!()
        .env("LC_ALL", "C")
        .env("TZ", "UTC")
        .arg("-d")
        .arg("@0")
        .arg("+%-N")
        .succeeds()
        .stdout_is("000000000\n");
}

Contributor guide

Tech stack
rust
Domain
cli
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Rust programming basicsstrftime format specifiers
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
85
Research direction
Investigate the strftime implementation in src/uu/date/src/date.rs (or related files). Understand how flags and widths are currently handled for other format specifiers. Implement similar logic for %N, ensuring that flags like ' ' for space padding and ' ' for no padding are respected, and that width specifiers truncate or pad as per GNU date. Use the provided test cases to verify correctness.