uutils/coreutils

date: strftime O modifier leaks as literal in C locale

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#11656 opened on Apr 5, 2026

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U - datefuzzinggood first issue

Description

Summary

date leaks the strftime O modifier as literal text (e.g. %Om → %om) while GNU strips it in C locale. The O modifier requests "alternative numeric symbols" and is a no-op under LC_ALL=C.

Found by a fuzz_date run.

Reproduction

$ LC_ALL=C TZ=UTC /usr/bin/date -d '2024-06-15' '+%Om-%Oy-%Ol'
06-24-12
$ echo $?
0

$ LC_ALL=C TZ=UTC target/debug/coreutils date -d '2024-06-15' '+%Om-%Oy-%Ol'
%Om-%Oy-%Ol
$ echo $?
0

The E modifier is similarly affected.

Test

#[test]
fn test_date_strftime_o_modifier() {
    new_ucmd!()
        .env("LC_ALL", "C")
        .env("TZ", "UTC")
        .arg("-d")
        .arg("2024-06-15")
        .arg("+%Om-%Oy-%Ol")
        .succeeds()
        .stdout_is("06-24-12\n");
}

Contributor guide

Tech stack
rustshell
Domain
cli
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
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 basicsdate formatting
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Investigate the strftime implementation in uutils/coreutils, focusing on how the 'O' and 'E' modifiers are handled. Look for the formatting logic in the date command, likely in `src/date/date.rs` or similar. The provided test can be used to verify the fix. Refer to GNU coreutils behavior where these modifiers are no ops in the C locale and should be stripped.