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19.1 Introduction

A filesystem stores a lot of additional information about files aside from their actual contents.

This information includes such particulars as the file's size, what directory it's in, and access

permissions for the file. If you're working with files, you may also need to manipulate this

metadata. PHP gives you a variety of functions to read and manipulate directories, directory

entries, and file attributes. Like other file-related parts of PHP, the functions are similar to the

C functions that accomplish the same tasks, with some simplifications.

Files are organized with inodes . Each file (and other parts of the filesystem, such as

directories, devices, and links) has its own inode. That inode contains a pointer to where the

file's data blocks are as well as all the metadata about the file. The data blocks for a directory

hold the names of the files in that directory and the inode of each file.

PHP provides two ways to look in a directory to see what files it holds. The first way is to use

opendir( )

to get a directory handle,

readdir( )

to iterate through the files, and

closedir( )

to close the directory handle:

$d = opendir('/usr/local/images') or die($php_errormsg);

while (false !== ($f = readdir($d))) {

// process file

}

closedir($d);

The second method is to use the directory class. Instantiate the class with

dir( )

, read

each filename with the

read( )

method, and close the directory with

close( )

$d = dir('/usr/local/images') or die($php_errormsg);

while (false !== ($f = $d->read())) {

// process file

}

$d->close();

Recipe 19.8

shows how to use

opendir( )

dir( )

to process each file in a

directory. Making new directories is covered in Recipe 19.11

and removing directories in

Recipe 19.12

The filesystem holds more than just files and directories. On Unix, it can also hold symbolic

links. These are special files whose contents are a pointer to another file. You can delete the

link without affecting the file it points to. To create a symbolic link, use

symlink( )

symlink('/usr/local/images','/www/docroot/images') or die($php_errormsg);

This creates a symbolic link called images in /www/docroot that points to /usr/local/images.

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To find information about a file, directory, or link you must examine its inode. The function

stat( )

retrieves the metadata in an inode for you. Recipe 19.3

discusses

stat( )

PHP also has many functions that use

stat( )

internally to give you a specific piece of

information about a file. These are listed in Table 19-1

Table 19-1. File information functions

Function name

What file information does the function provide?

file_exists( )

Does the file exist?

fileatime( )

Last access time

filectime( )

Last metadata change time

filegroup( )

Group (numeric)

fileinode( )

Inode number

filemtime( )

Last change time of contents

fileowner( )

Owner (numeric)

fileperms( )

Permissions (decimal, numeric)

filesize( )

Size

filetype( )

Type (fifo, char, dir, block, link, file, unknown)

is_dir( )

Is it a directory?

is_executable( )

Is it executable?

is_file( )

Is it a regular file?

is_link( )

Is it a symbolic link?

is_readable( )

Is it readable?

is_writable( )

Is it writeable?

On Unix, the file permissions indicate what operations the file's owner, users in the file's

group, and all users can perform on the file. The operations are reading, writing, and

executing. For programs, executing means the ability to run the program; for directories, it's

the ability to search through the directory and see the files in it.

Unix permissions can also contain a setuid bit, a setgid bit, and a sticky bit. The setuid bit

means that when a program is run, it runs with the user ID of its owner. The setgid bit means

that a program runs with the group ID of its group. For a directory, the setgid bit means that

new files in the directory are created by default in the same group as the directory. The sticky

bit is useful for directories in which people share files because it prevents nonsuperusers with

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write permission in a directory from deleting files in that directory unless they own the file or

the directory.

When setting permissions with

chmod( )

(see Recipe 19.4

), they must be expressed as an

octal number. This number has four digits. The first digit is any special setting for the file

(such as setuid or setgid). The second digit is the user permissions — what the file's owner

can do. The third digit is the group permissions — what users in the file's group can do. The

fourth digit is the world permissions — what all other users can do. To compute the

appropriate value for each digit, add together the permissions you want for that digit using the

values in Table 19-2

. For example, a permission value of

0644

means that there are no

special settings (the

), the file's owner can read and write the file (the

, which is

(read)

(write)), users in the file's group can read the file (the first

), and all other users can

also read the file (the second

). A permission value of

4644

is the same, except that the

file is also setuid.

Table 19-2. File permission values

Value

Permission meaning

Special setting meaning

Read

setuid

Write

setgid

Execute

sticky

The permissions of newly created files and directories are affected by a setting called the

umask, which is a permission value that is removed, or masked out, from the initial

permissions of a file (

0666

or directory (

0777

). For example, if the umask is

0022

, the

default permissions for a new file created with

touch( )

fopen( )

are

0644

and

the default permissions for a new directory created with

mkdir( )

are

0755

. You can get

and set the umask with the function

umask( )

. It returns the current umask and, if an

argument is supplied to it, changes the umask to the value of that argument. For example,

here's how to make the permissions on newly created files prevent anyone but the file's owner

(and the superuser) from accessing the file:

$old_umask = umask(0077);

touch('secret-file.txt');

umask($old_umask);

The first call to

umask( )

masks out all permissions for group and world. After the file is

created, the second call to

umask( )

restores the umask to the previous setting. When

PHP is run as a server module, it restores the umask to its default value at the end of each

request. Like other permissions-related functions,

umask( )

doesn't work on Windows.

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Recipe 19.2 Getting and Setting File

Timestamps

19.2.1 Problem

You want to know when a file was last accessed or changed, or you want to update a file's

access or change time; for example, you want each page on your web site to display when it

was last modified.

19.2.2 Solution

The

fileatime( )

filemtime( )

, and

filectime( )

functions return the

time of last access, modification, and metadata change of a file:

$last_access = fileatime('larry.php');

$last_modification = filemtime('moe.php');

$last_change = filectime('curly.php');

The

touch( )

function changes a file's modification time:

touch('shemp.php'); // set modification time to now

touch('joe.php',$timestamp); // set modification time to $timestamp

19.2.3 Discussion

The

fileatime( )

function returns the last time a file was opened for reading or

writing. The

filemtime( )

function returns the last time a file's contents were changed.

The

filectime( )

function returns the last time a file's contents or metadata (such as

owner or permissions) were changed. Each function returns the time as an epoch timestamp.

A file's modification time can be updated with

touch( )

. Without a second argument,

touch( )

sets the modification time to the current date and time. To set a file's

modification time to a specific value, pass that value as an epoch timestamp to

touch( )

as a second argument.

This code prints the time a page on your web site was last updated:

print "Last Modified:

".strftime('%c',filemtime($_SERVER['SCRIPT_FILENAME']));

19.2.4 See Also

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Documentation on

fileatime( )

at http://www.php.net/fileatime

filemtime( )

at http://www.php.net/filemtime

, and

filectime( )

at http://www.php.net/filectime

Recipe 19.3 Getting File Information

19.3.1 Problem

You want to read a file's metadata; for example, permissions and ownership.

19.3.2 Solution

Use

stat( )

, which returns an array of information about a file:

$info = stat('harpo.php');

19.3.3 Discussion

The function

stat( )

returns an array with both numeric and string indexes with

information about a file. The elements of this array are in Table 19-3

Table 19-3. Information returned by stat( )

Numeric index String index

Value

dev

Device

ino

Inode

mode

Permissions

nlink

Link count

uid

Owner's user ID

gid

Group's group ID

rdev

Device type for inode devices (-1 on Windows)

size

Size (in bytes)

atime

Last access time (epoch timestamp)

mtime

Last change time of contents (epoch timestamp)

ctime

Last change time of contents or metadata (epoch timestamp)

blksize

Block size for I/O (-1 on Windows)

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Number of block allocated to this file

The mode element of the returned array contains the permissions expressed as a base 10

integer. This is confusing since permissions are usually either expressed symbolically (e.g., ls's

-rw-r--r--

output) or as an octal integer (e.g.,

0644

). To convert the permissions to a

more understandable format, use

base_convert( )

to change the permissions to

octal:

$file_info = stat('/tmp/session.txt');

$permissions = base_convert($file_info['mode'],10,8);

This results in a six-digit octal number. For example, if ls displays the following about

/tmp/session.txt:

-rw-rw-r-- 1 sklar sklar 12 Oct 23 17:55 /tmp/session.txt

Then

$file_info['mode']

33204

and

$permissions

100664

. The

last three digits (

664

) are the user (read and write), group (read and write), and other

(read) permissions for the file. The third digit,

, means that the file is not setuid or setgid.

The leftmost

means that the file is a regular file (and not a socket, symbolic link, or other

special file).

Because

stat( )

returns an array with both numeric and string indexes, using

foreach

to iterate through the returned array produces two copies of each value. Instead,

use a

for

loop from element 0 to element 12 of the returned array.

Calling

stat( )

on a symbolic link returns information about the file the symbolic link

points to. To get information about the symbolic link itself, use

lstat( )

Similar to

stat( )

fstat( )

, which takes a file handle (returned from

fopen(

)

popen( )

) as an argument. You can use

fstat( )

only on local files, however,

not URLs passed to

fopen( )

PHP's

stat( )

function uses the underlying stat(2) system call, which is expensive. To

minimize overhead, PHP caches the result of calling stat(2). So, if you call

stat( )

on a

file, change its permissions, and call

stat( )

on the same file again, you get the same

results. To force PHP to reload the file's metadata, call

clearstatcache( )

, which

flushes PHP's cached information. PHP also uses this cache for the other functions that return

file metadata:

file_exists( )

fileatime( )

filectime( )

filegroup( )

fileinode( )

filemtime( )

fileowner( )

fileperms( )

filesize( )

filetype( )

fstat( )

is_dir( )

is_executable( )

is_file( )

is_link( )

is_readable( )

is_writable( )

, and

lstat( )

19.3.4 See Also

Documentation on

stat( )

at http://www.php.net/stat

lstat( )

http://www.php.net/lstat

fstat( )

at http://www.php.net/fstat

, and

clearstatcache( )

at http://www.php.net/clearstatcache

Recipe 19.4 Changing File Permissions or

Ownership

19.4.1 Problem

You want to change a file's permissions or ownership; for example, you want to prevent other

users from being able to look at a file of sensitive data.

19.4.2 Solution

Use

chmod( )

to change the permissions of a file:

chmod('/home/user/secrets.txt',0400);

Use

chown( )

to change a file's owner and

chgrp( )

to change a file's group:

chown('/tmp/myfile.txt','sklar'); // specify user by name

chgrp('/home/sklar/schedule.txt','soccer'); // specify group by name

chown('/tmp/myfile.txt',5001); // specify user by uid

chgrp('/home/sklar/schedule.txt',102); // specify group by gid

19.4.3 Discussion

The permissions passed to

chmod( )

must be specified as an octal number.

The superuser can change the permissions, owner, and group of any file. Other users are

restricted. They can change only the permissions and group of files that they own, and can't

change the owner at all. Nonsuperusers can also change only the group of a file to a group

they belong to.

The functions

chmod( )

chgrp( )

, and

chown( )

don't work on Windows.

19.4.4 See Also

Documentation on

chmod( )

at http://www.php.net/chmod

chown( )

http://www.php.net/chown

, and

chgrp( )

at http://www.php.net/chgrp

Recipe 19.5 Splitting a Filename into Its

Component Parts

19.5.1 Problem

You want to find a file's path and filename; for example, you want to create a file in the same

directory as an existing file.

19.5.2 Solution

Use

basename( )

to get the filename and

dirname( )

to get the path:

$full_name = '/usr/local/php/php.ini';

$base = basename($full_name); // $base is php.ini

$dir = dirname($full_name); // $dir is /usr/local/php

Use

pathinfo( )

to get the directory name, base name, and extension in an associative

array:

$info = pathinfo('/usr/local/php/php.ini');

19.5.3 Discussion

To create a temporary file in the same directory as an existing file, use

dirname( )

find the directory, and pass that directory to

tempnam( )

$dir = dirname($existing_file);

$temp = tempnam($dir,'temp');

$temp_fh = fopen($temp,'w');

The elements in the associative array returned by

pathinfo( )

are

dirname

basename

, and

extension

$info = pathinfo('/usr/local/php/php.ini');

print_r($info);

Array

(

[dirname] => /usr/local/php

[basename] => php.ini

[extension] => ini

)

You can also pass

basename( )

an optional suffix to remove it from the filename. This

sets

$base

to php:

$base = basename('/usr/local/php/php.ini','.ini');

Using functions such as

basename( )

dirname( )

, and

pathinfo( )

is more

portable than just separating a full filename on

because they use an operating-system

appropriate separator. On Windows, these functions treat both

and

as file and directory

separators. On other platforms, only

is used.

There's no built-in PHP function to combine the parts produced by

basename( )

dirname( )

, and

pathinfo( )

back into a full filename. To do this you have to

combine the parts with . and

$dirname = '/usr/local/php';

$basename = 'php';

$extension = 'ini';

$full_name = $dirname . '/' . $basename . '.' . $extension;

You can pass a full filename produced like this to other PHP file functions on Windows, because

PHP accepts

as a directory separator on Windows.

19.5.4 See Also

Documentation on

basename( )

at http://www.php.net/basename

dirname( )

http://www.php.net/dirname

, and

pathinfo( )

at http://www.php.net/pathinfo

Recipe 19.6 Deleting a File

19.6.1 Problem

You want to delete a file.

19.6.2 Solution

Use

unlink( )

unlink($file) or die ("can't delete $file: $php_errormsg");

19.6.3 Discussion

The function

unlink( )

is only able to delete files that the user of the PHP process is able

to delete. If you're having trouble getting

unlink( )

to work, check the permissions on

the file and how you're running PHP.

19.6.4 See Also

Documentation on

unlink( )

at http://www.php.net/unlink

Recipe 19.7 Copying or Moving a File

19.7.1 Problem

You want to copy or move a file.

19.7.2 Solution

Use

copy( )

to copy a file:

copy($old,$new) or die("couldn't copy $old to $new: $php_errormsg");

Use

rename( )

to move a file:

rename($old,$new) or die("couldn't move $old to $new: $php_errormsg");

19.7.3 Discussion

On Unix,

rename( )

can't move files across filesystems. To do so, copy the file to the new

location and then delete the old file:

if (copy("/tmp/code.c","/usr/local/src/code.c")) {

unlink("/tmp/code.c");

}

If you have multiple files to copy or move, call

copy( )

rename( )

in a loop. You

can operate only on one file each time you call these functions.

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