PHP file_exists(), is_file(), unlink() and rename()

Before you read or change a file, check that it is there and that you may use it.

Does it exist?

index.php

PHP

<?php
file_put_contents("data.txt", "x");

var_dump(file_exists("data.txt"));
var_dump(file_exists("nothing.txt"));

Output

OUTPUT

1
2

bool(true)
bool(false)

file_exists() is true for files and folders. To be precise, use these:

Function	True when
`is_file($p)`	It is a regular file
`is_dir($p)`	It is a folder
`is_readable($p)`	PHP may read it
`is_writable($p)`	PHP may write to it

index.php

PHP

<?php
mkdir("folder");
file_put_contents("data.txt", "x");

var_dump(is_file("data.txt"));
var_dump(is_file("folder"));
var_dump(is_dir("folder"));
var_dump(is_readable("data.txt"));

Output

OUTPUT

bool(true)
bool(false)
bool(true)
bool(true)

Delete a file: unlink()

index.php

PHP

<?php
file_put_contents("temp.txt", "x");

if (is_file("temp.txt")) {
    unlink("temp.txt");
}

var_dump(file_exists("temp.txt"));

Output

OUTPUT

bool(false)

Rename or move: rename()

index.php

PHP

<?php
file_put_contents("old-name.txt", "x");

rename("old-name.txt", "new-name.txt");

var_dump(file_exists("old-name.txt"), file_exists("new-name.txt"));

Output

OUTPUT

1
2

bool(false)
bool(true)

rename() also moves a file to another folder.

Copy: copy()

index.php

PHP

<?php
file_put_contents("original.txt", "content");

copy("original.txt", "backup.txt");

echo file_get_contents("backup.txt");

Output

OUTPUT

content

Race conditions

Checking first and acting later has a small gap. Another process could delete the file in between.

index.php

PHP

<?php
if (file_exists($file)) {        // check
    $data = file_get_contents($file);   // use: the file might be gone now
}

For important code, just try the action and handle failure:

index.php

PHP

<?php
$data = @file_get_contents("maybe-missing.txt");

if ($data === false) {
    echo "File not available";
}

Output

OUTPUT

File not available

Temporary files

index.php

PHP

<?php
$temp = tempnam(sys_get_temp_dir(), "demo_");

file_put_contents($temp, "short-lived");
echo file_get_contents($temp) . "\n";

unlink($temp);
var_dump(file_exists($temp));

Output

OUTPUT

1
2

short-lived
bool(false)

tempnam() creates a unique file in a folder you choose, which is safe from name clashes.

dangerous

Deleting with user input

unlink($_GET["file"]) lets a visitor delete any file PHP may touch. Never build a path from input. Use IDs mapped to files you stored yourself.