gchq/CyberChef · error · OperationError

'Take every' must be a positive integer.

Error message

'Take every' must be a positive integer.

What it means

Take Nth Bytes requires the 'Take every' argument (n) to be a positive integer. The guard `parseInt(n,10) !== n || n <= 0` rejects non-integers and values <= 0 before the sampling loop runs, because a non-positive or fractional stride is meaningless for byte selection.

Source

Thrown at src/core/operations/TakeNthBytes.mjs:57

                name: "Apply to each line",
                type: "boolean",
                value: false
            }
        ];
    }

    /**
     * @param {byteArray} input
     * @param {Object[]} args
     * @returns {byteArray}
     */
    run(input, args) {
        const n = args[0];
        const start = args[1];
        const eachLine = args[2];

        if (parseInt(n, 10) !== n || n <= 0) {
            throw new OperationError("'Take every' must be a positive integer.");
        }
        if (parseInt(start, 10) !== start || start < 0) {
            throw new OperationError("'Starting at' must be a positive or zero integer.");
        }

        let offset = 0;
        const output = [];
        for (let i = 0; i < input.length; i++) {
            if (eachLine && input[i] === 0x0a) {
                output.push(0x0a);
                offset = i + 1;
            } else if (i - offset >= start && (i - (start + offset)) % n === 0) {
                output.push(input[i]);
            }
        }

        return output;
    }

View on GitHub (pinned to 4290ea7539)

Solutions

1. Enter a positive integer such as 1, 2, or 5 for 'Take every'.
2. Use 1 to keep every byte from the start offset onward.
3. Confirm no decimal point or negative sign is present in the field.

Example fix

// before: args[0] (Take every) = 0   -> throws
// after:  args[0] (Take every) = 2   -> keeps every 2nd byte

const n = args[0];
if (!(Number.isInteger(n) && n > 0)) {
  throw new Error("'Take every' must be a positive integer");
}

const isPositiveInt = v => Number.isInteger(v) && v > 0;

try { takeNthBytes(input, n, start, eachLine); }
catch (e) { if (/Take every/.test(e.message)) { /* set n to a positive int */ } else throw e; }

When it happens

Trigger: Passing a non-integer (e.g. 2.5) or a non-positive value (0, -1) for the 'Take every' argument. Also triggered by NaN or string values that fail the parseInt identity check.

Common situations: Leaving the field blank (defaults to an invalid value), entering 0 meaning 'take nothing', or pasting a decimal where an integer is expected.

Related errors

• 'Starting at' must be a positive or zero integer.
• Width must be a positive integer
• ${this.name} must be an integer.
• Byte length must be a positive integer
• L must be non-negative

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/774f798d18e31637. Report an issue: GitHub.