php-fixed-length-file-parser

A parser class for handling fixed length text files in PHP.

Fixed Length Files (aka poor man's CSV) are plain text files with one data set per row but without any delimiter:

01Amy  BLUES
02Bob  REDS

Installation

composer require fanatique/php-fixed-length-file-parser

Features

• Register a chopping map to define field positions and lengths
• Register a pre-flight check to filter lines before parsing
• Register a callback to transform each parsed line
• Supports any callable (closures, invokable objects, static methods, etc.)
• Memory-efficient line-by-line reading — safe for very large files

Usage

The following example shows how to transform a fixed length file into an associative array. A working example can be found in example/parsing.php.

<?php

declare(strict_types=1);

require_once __DIR__ . '/vendor/autoload.php';

$parser = new \Fanatique\Parser\FixedLengthFileParser();

// Set the chopping map (aka where to extract the fields)
$parser->setChoppingMap([
    ['field_name' => 'id', 'start' => 0, 'length' => 2],
    ['field_name' => 'name', 'start' => 2, 'length' => 5, 'align' => 'left'],
    ['field_name' => 'team', 'start' => 7, 'length' => 5],
]);

// Set the absolute path to the file
$parser->setFilePath(__DIR__ . '/example.dat');

// Parse the file
try {
    $parser->parse();
} catch (\Fanatique\Parser\ParserException $e) {
    echo 'ERROR - ' . $e->getMessage() . PHP_EOL;
    exit(1);
}

// Get the content
var_dump($parser->getContent());

field_name and length are required. start is optional — if omitted, it is calculated from the previous entry's start + length. align is optional and configures which padding spaces to trim: 'left' (removes trailing), 'right' (removes leading), or 'both' (the default).

Registering a pre-flight check

A pre-flight check can be registered to filter each row before it is parsed. The callable receives the raw line as a string and must return a boolean:

• true → parse the line
• false → skip the line

$parser->setPreflightCheck(function (string $line): bool {
    // Skip lines starting with a comment character
    return !str_starts_with($line, '#');
});

Registering a callback

A callback is applied to each line after parsing. It receives the parsed line as an associative array and must return an array of the same format:

$parser->setCallback(function (array $line): array {
    $line['team'] = ucwords(strtolower($line['team']));
    return $line;
});

Using invokable objects

Since the parser accepts any callable, you can use invokable objects for more complex or reusable logic:

class TeamNormalizer
{
    public function __invoke(array $line): array
    {
        $line['team'] = ucwords(strtolower($line['team']));
        return $line;
    }
}

$parser->setCallback(new TeamNormalizer());

Development

# Install dependencies
composer install

# Run tests
composer test

# Run static analysis
composer phpstan

License

MIT — see LICENSE for details.