sharkdp/fd · error · anyhow::Error

' ' is not a valid size constraint. See 'fd --help'.

Error message

'{}' is not a valid size constraint. See 'fd --help'.

What it means

SizeFilter::from_string (filter/size.rs:30) requires the --size value to match the regex (?i)^([+-]?)(\d+)(b|[kmgt]i?b?)$. The optional sign selects Min (+) or Max (-); the unit must be one of b/k/m/g/t in SI or ki/mi/gi/ti binary forms. Anything not matching (e.g. bare number, bad unit, negative number without sign usage) yields this error.

Solutions

1. Add a recognized unit: `fd --size 5k`, `fd --size +10m`, `fd --size -1g`, `fd --size 100b`.
2. For 'larger than' prefix '+', for 'smaller than' prefix '-', for exact omit the sign.
3. Use binary units if needed: `fd --size 1mi`, `fd --size 2gi`.

Example fix

# before
fd --size 5

# after
fd --size 5k      # exactly 5 KB
fd --size +10m   # at least 10 MB
fd --size -1g    # less than 1 GB

validate_size() {
  # pattern: optional +/-, integer, unit b|k|ki|m|mi|g|gi|t|ti(+b)
  printf '%s' "$1" | grep -Eq '^[+-]?[0-9]+(b|k|ki|m|mi|g|gi|t|ti)b?$' && fd --size "$1"
}

When it happens

Trigger: Passing `fd --size 5` (no unit), `fd --size 5x`, `fd --size abc`, `fd --size 1.5k` (decimals not supported), or `fd --size kb` (missing magnitude). The regex requires an integer magnitude and a recognized unit.

Common situations: Forgetting the unit; using a decimal point; typing unsupported units like 'pb'/bytes-only with no suffix; confusing fd's syntax with du/find -size syntax.

Related errors

• ' ' is not a valid date or duration. See 'fd --help'.
• Malformed exclude pattern
• more than one ':' present in owner string
• Note: You can search for literal substrings with…
• A path separator must be exactly one byte, but the given…

AI-assisted analysis of sharkdp/fd@ee20f426dd (2026-08-09). Data as JSON: /api/errors/0306286966815afd. Report an issue: GitHub.

Appendix: source

Thrown at src/filter/size.rs:30

    Equals(u64),
}

// SI prefixes (powers of 10)
const KILO: u64 = 1000;
const MEGA: u64 = KILO * 1000;
const GIGA: u64 = MEGA * 1000;
const TERA: u64 = GIGA * 1000;

// Binary prefixes (powers of 2)
const KIBI: u64 = 1024;
const MEBI: u64 = KIBI * 1024;
const GIBI: u64 = MEBI * 1024;
const TEBI: u64 = GIBI * 1024;

impl SizeFilter {
    pub fn from_string(s: &str) -> anyhow::Result<Self> {
        SizeFilter::parse_opt(s)
            .ok_or_else(|| anyhow!("'{}' is not a valid size constraint. See 'fd --help'.", s))
    }

    fn parse_opt(s: &str) -> Option<Self> {
        let pattern =
            SIZE_CAPTURES.get_or_init(|| Regex::new(r"(?i)^([+-]?)(\d+)(b|[kmgt]i?b?)$").unwrap());
        if !pattern.is_match(s) {
            return None;
        }

        let captures = pattern.captures(s)?;
        let limit_kind = captures.get(1).map_or("+", |m| m.as_str());
        let quantity = captures
            .get(2)
            .and_then(|v| v.as_str().parse::<u64>().ok())?;

        let multiplier = match &captures.get(3).map_or("b", |m| m.as_str()).to_lowercase()[..] {
            v if v.starts_with("ki") => KIBI,
            v if v.starts_with('k') => KILO,

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