Writer connection

The League\Csv\Writer class extends the general connections capabilities to create or update a CSV document.

When inserting records into a CSV document using League\Csv\Writer, first insert all the data that need to be inserted before starting manipulating the CSV. If you manipulate your CSV document before insertion, you may change the file cursor position and erase your data.

Inserting records

public Writer::insertOne(array $record): int
public Writer::insertAll(iterable $records): int

Writer::insertOne inserts a single record into the CSV document while Writer::insertAll adds several records. Both methods return the length of the written data.

Writer::insertOne takes a single argument, an array which represents a single CSV record. Writer::insertAll takes a single argument a PHP iterable which contains a collection of CSV records.

use League\Csv\Writer;

$records = [
    [1, 2, 3],
    ['foo', 'bar', 'baz'],
    ['john', 'doe', 'john.doe@example.com'],

$writer = Writer::createFromPath('/path/to/saved/file.csv', 'w+');
$writer->insertOne(['john', 'doe', 'john.doe@example.com']);
$writer->insertAll($records); //using an array
$writer->insertAll(new ArrayIterator($records)); //using a Traversable object

In the above example, all CSV records are saved to /path/to/saved/file.csv

If the record can not be inserted into the CSV document a League\Csv\CannotInsertRecord exception is thrown. This exception extends League\Csv\Exception and adds the ability to get the record on which the insertion failed.

use League\Csv\CannotInsertRecord;
use League\Csv\Writer;

$records = [
    [1, 2, 3],
    ['foo', 'bar', 'baz'],
    ['john', 'doe', 'john.doe@example.com'],

try {
    $writer = Writer::createFromPath('/path/to/saved/file.csv', 'r');
} catch (CannotInsertRecord $e) {
    $e->getRecord(); //returns [1, 2, 3]

Since version 9.2.0 you can provide an empty string for the escape character to enable better RFC4180 compliance.

use League\Csv\Writer;

$record = ['"foo"', 'foo bar', 'baz ', 'foo\\"bar'];

$writer = Writer::createFromString();
echo $writer->toString();
// """foo""","foo bar","baz ","foo\"bar"
// """foo""","foo bar","baz ","foo\""bar"

The addition of this new feature means the deprecation of RFC4180Field.

You still need to set the newline sequence as shown below

Handling newline

Because PHP’s fputcsv implementation has a hardcoded \n, we need to be able to replace the last LF code with one supplied by the developer for more interoperability between CSV packages on different platforms. The newline sequence will be appended to each newly inserted CSV record.


public Writer::setNewline(string $sequence): self
public Writer::getNewline(void): string


use League\Csv\Writer;

$writer = Writer::createFromFileObject(new SplFileObject());
$newline = $writer->getNewline(); //equals "\n";
$newline = $writer->getNewline(); //equals "\r\n";
$writer->insertOne(["one", "two"]);
echo $writer->toString(); //displays "one,two\r\n";

The default newline sequence is \n;

If you are using a non-seekable CSV document, changing the newline character will trigger an exception.

Flushing the buffer

For advanced usages, you can now manually indicate when the flushing mechanism occurs while adding new content to your CSV document.


public Writer::setFlushThreshold(?int $treshold): self
public Writer::getFlushThreshold(void): ?int

By default, getFlushTreshold returns null.

Writer::insertAll always flushes its buffer when all records are inserted, regardless of the threshold value.

If set to null the inner flush mechanism of PHP's fputcsv will be used.

Records filtering

public Writer::addFormatter(callable $callable): Writer
public Writer::addValidator(callable $callable, string $validatorName): Writer

Sometimes you may want to format and/or validate your records prior to their insertion into your CSV document. The Writer class provides a formatter and a validator mechanism to ease these operations.


Record Formatter

A formatter is a callable which accepts a single CSV record as an array on input and returns an array representing the formatted CSV record according to its inner rules.

function(array $record): array

Adding a Formatter to a Writer object

You can attach as many formatters as you want to the Writer class using the Writer::addFormatter method. Formatters are applied following the First In First Out rule.

use League\Csv\Writer;

$formatter = function (array $row): array {
    return array_map('strtoupper', $row);
$writer = Writer::createFromFileObject(new SplTempFileObject());
$writer->insertOne(['john', 'doe', 'john.doe@example.com']);

echo $writer->toString();


Record Validator

A validator is a callable which takes a single CSV record as an array as its sole argument and returns a boolean to indicate if it satisfies the validator’s inner rules.

function(array $record): bool

The validator must return true to validate the submitted record.

Any other expression, including truthy ones like yes, 1,… will make the insertOne method throw an League\Csv\CannotInsertRecord exception.

Adding a Validator to a Writer object

As with the formatter capabilities, you can attach as many validators as you want using the Writer::addValidator method. Validators are applied following the First In First Out rule.

The CSV record is checked against your supplied validators after it has been formatted.

Writer::addValidator takes two (2) required parameters:

On failure a League\Csv\CannotInsertRecord exception is thrown. This exception will give access to:

use League\Csv\Writer;
use League\Csv\CannotInsertRecord;

$writer->addValidator(function (array $row): bool {
    return 10 == count($row);
}, 'row_must_contain_10_cells');

try {
    $writer->insertOne(['john', 'doe', 'john.doe@example.com']);
} catch (CannotInsertRecord $e) {
    echo $e->getName(); //displays 'row_must_contain_10_cells'
    $e->getData();//returns the invalid data ['john', 'doe', 'john.doe@example.com']