Quick Tip: How To Read a Local File with PHP

PHP provides three native functions for local file operations: file(), file_get_contents() and fopen(). Although complete libraries are built around these functions, they are still the preferred method of quickly manipulating PHP files.

We will first understand the functions of these functions and then look at their working examples.

file() and file_get_contents()

file() and file_get_contents() work very similarly. They all read the entire file. However, file() reads the file into an array, while file_get_contents() reads the file into a string. Both functions are binary safe, meaning they can be used for any type of file content.

Be extra careful when using file(), because the array it returns will be separated by newlines, but each element will still be attached with a terminating newline.

fopen()

fopen() Functions work completely differently. It will open a file descriptor that acts as a stream to read or write to the file.

The PHP manual explains this:

In its simplest form, a stream is a resource object that exhibits streamable behavior. That is, it can be read or written from it in a linear manner, and it may be possible to jump to anywhere in the stream using fseek().

Simply put, calling fopen() will not do anything, it will only open a stream.

When you open the stream and have the file handle, you can use other functions such as fread() and fwrite() to manipulate the file. Once done, you can use fclose() to close the stream.

Example

View the following example:

<?php
    $filepath = "/usr/local/sitepoint.txt";
    $handle = fopen($filename, "r");
    $contents = fread($handle, filesize($filename));
    fclose($handle);

The above functions will give you more granular control over the files, but they are much lower than the file() or file_get_contents() functions, which is preferable as stated in the PHP documentation:

file_get_contents() is the preferred method for reading file contents to strings. If your operating system supports it, it will use memory swap technology to improve performance.

file_get_contents() It's quite easy to use:

<?php
    $file_contents = file_get_contents('./file.txt');

This will read the content of file.txt into $file_contents.

If we only need a part of the file, we can do this:

<?php
    $file_contents = file_get_contents('./file.txt', FALSE, NULL, 20, 14);

This will read file.txt 14 characters starting from the 20th character. For more information on all parameters of file_get_contents(), please refer to the official documentation.

FAQ for Reading Local Files in PHP

What is the difference between

file_get_contents() and fopen() in PHP?

file_get_contents() and fopen() are both used to read files in PHP, but they work slightly differently. file_get_contents() Read the file into a string and return the entire file as a single string. This function is simple and easy to use, but is not suitable for large files, as it can consume a lot of memory. On the other hand, fopen() opens a file or URL and returns a resource that can be used with other file-related functions such as fgets() or fwrite(). This function is more flexible and efficient for large files because it reads the files line by line.

How to handle errors when reading files in PHP?

PHP provides several ways to handle errors when reading files. A common approach is to use the "@" operator before the function to suppress error messages. Another way is to use the file_exists() function to check if the file exists before trying to read it. You can also use the is_readable() function to check if the file is readable. If an error occurs, these functions will return false, allowing you to handle the error gracefully.

Can I read files from a remote server in PHP?

Yes, PHP allows you to read files from a remote server using the file_get_contents() or fopen() functions (using a URL instead of a local file path). However, for security reasons, this feature may be disabled on some servers. You can check if it is enabled by viewing the php.ini settings in the allow_url_fopen file.

How to read a specific line of a file in PHP?

PHP does not provide built-in functions to read specific lines of a file, but you can do this by reading the file into an array using the file() function and then accessing the required lines by indexing it. Remember that the index starts at 0, so the first row is at index 0, the second row is at index 1, and so on.

How to read files in binary mode in PHP?

To read files in binary mode in PHP, you can use the fopen() function with the "b" flag. This is especially useful for reading binary files such as images or executables. After opening the file, you can read it using the fread() function, which returns the data as a binary string.

How to read CSV files in PHP?

PHP provides the fgetcsv() function to read CSV files. This function parses the CSV format field of the rows it reads and returns an array of read fields. You can use this function for loops to read the entire CSV file.

How to reversely read a file in PHP?

PHP does not provide built-in functions to read files in reverse, but you can do this by reading files into an array using the file() function, and then reverse the array using the array_reverse() function.

How to read a file in PHP without locking it?

By default, PHP does not lock files when reading them. However, if you need to make sure that the file is not locked, you can use the LOCK_SH function with the flock() flag before reading the file. This function will attempt to acquire the shared lock, allowing other processes to read the file at the same time.

How to efficiently read large files in PHP?

To read large files efficiently in PHP, you can use the fopen() function to open the file and then use the fgets() function in the loop to read the file line by line. This method is more memory-saving than reading the entire file into a string or an array, since it only saves the current line in memory.

How to read files in PHP and output content to the browser?

To read files in PHP and output content to the browser, you can use the readfile() function. This function reads the file and writes it to the output buffer, and then sends it to the browser. This is a convenient way to provide files (such as images or downloadable files) to the user.

The above is the detailed content of Quick Tip: How To Read a Local File with PHP. For more information, please follow other related articles on the PHP Chinese website!