Reading, writing, and checking files on the server.
Understanding file handling in PHP
File handling means reading from and writing to files on the server – logs, config files, user uploads, CSV exports, that sort of thing.
Opening a file
Before you read or write, open the file with fopen(). You pass the file path and a mode:
File open modes
'r': open for reading only; start at the beginning of the file.'w': open for writing only; start at the beginning and truncate the file to zero length. Creates the file if it does not exist.'a': open for writing only; start at the end of the file. Creates the file if it does not exist.
Example:
<?php
$file = fopen("example.txt", "r") or die("Unable to open file!");
?>Reading from a file
Once a file is open, several functions can read its contents:
Using fread()
Reads up to a specified number of bytes:
<?php
echo fread($file, filesize("example.txt"));
fclose($file);
?>Using fgets()
Reads one line at a time:
<?php
echo fgets($file);
fclose($file);
?>Writing to a file
Use fwrite() or the shorter file_put_contents():
Using fwrite()
Writes a string to an open file handle:
<?php
$file = fopen("newfile.txt", "w") or die("Unable to open file!");
$txt = "Hello, PHP World!\n";
fwrite($file, $txt);
fclose($file);
?>Using file_put_contents()
Combines fopen(), fwrite(), and fclose() in one call:
<?php
file_put_contents("newfile.txt", "Hello, PHP World!", FILE_APPEND);
?>Appending to a file
To add content without wiping what’s already there, open in append mode ('a'):
<?php
$file = fopen("newfile.txt", "a") or die("Unable to open file!");
$txt = "Adding more content.\n";
fwrite($file, $txt);
fclose($file);
?>Checking for file existence and size
Worth checking before you read or write:
Using file_exists()
<?php
if(file_exists("example.txt")) {
echo "File exists.";
} else {
echo "File does not exist.";
}
?>Using filesize()
<?php
echo "File size is " . Filesize("example.txt") . " bytes";
?>Deleting a file
Remove a file with unlink():
<?php
if (file_exists("deletefile.txt")) {
unlink("deletefile.txt");
echo "File deleted.";
} else {
echo "File does not exist.";
}
?>Working with CSV files
PHP handles CSV (comma-separated values) files too – common for spreadsheets and simple data exports:
Reading from a CSV file
<?php
$file = fopen("example.csv", "r");
while (($data = fgetcsv($file, 1000, ",")) !== FALSE) {
print_r($data);
}
fclose($file);
?>Writing to a CSV file
<?php
$list = array(
array('Alice', 'Doe', 'alice@example.com'),
array('Bob', 'Smith', 'bob@example.com')
);
$file = fopen('users.csv', 'w');
foreach ($list as $fields) {
fputcsv($file, $fields);
}
fclose($file);
?>Best practices and security
A few habits worth keeping:
- Validate and sanitise inputs when reading and writing files.
- Check file types and sizes on uploads.
- Handle errors gracefully when a file cannot be opened or read.
- Be careful with file paths to avoid directory traversal attacks.
File handling turns up everywhere in PHP – logs, config, exports, uploads. These functions cover the everyday read/write cases.