Using PHP fgets() to Read Files Line by Line

PHP fgets() Function Overview

fgets() reads a line from an opened file resource or a filename, optionally limiting the maximum number of bytes per read.

<code>fgets(file,length)</code>

The file parameter is a file handle, and length is optional; if omitted, PHP reads until a newline or EOF.

1. Reading a line from a file

Typical usage opens a file with fopen() , then loops until feof() while calling fgets() to retrieve each line.

<code>$file = fopen("data.txt", "r");
while (!feof($file)) {
    $line = fgets($file);
    echo $line;
}
fclose($file);
</code>

2. Specifying maximum bytes per read

Providing the optional length argument limits the number of bytes returned; for example, setting it to 1024 reads up to 1024 bytes per call.

<code>$file = fopen("data.txt", "r");
while (!feof($file)) {
    $line = fgets($file, 1024);
    echo $line;
}
fclose($file);
</code>

3. Reading binary files

When reading binary data, open the file in binary mode (e.g., "rb" ) and use fgets() to obtain each line, remembering that binary streams may contain newline characters.

<code>$file = fopen("image.jpg", "rb");
while (!feof($file)) {
    $data = fgets($file);
    // process $data
}
fclose($file);
</code>

4. Error handling

Check the result of fopen() before reading; if the file cannot be opened, fgets() will not be called and an error message can be displayed.

<code>$file = fopen("data.txt", "r");
if ($file) {
    while (!feof($file)) {
        $line = fgets($file);
        // process $line
    }
    fclose($file);
} else {
    echo "Failed to open file";
}
</code>

Summary

The fgets() function is a versatile tool for reading text or binary files line by line in PHP, offering optional byte limits and straightforward error handling, which helps improve file‑processing efficiency and reliability.