Opening and Closing Files
Files are opened in PHP using the
fopen command. The command takes two parameters, the file to be opened, and the mode in which to open the file. The function returns a file pointer if successful, otherwise zero (false). Files are opened with
fopen for reading or writing.
$fp = fopen("myfile.txt", "r");
If
fopen is unable to open the file, it returns 0. This can be used to exit the function with an appropriate message.
if ( !($fp = fopen("myfile.txt", "r") ) )
exit("Unable to open the input file.");
FileModes
The following table shows the different modes the file may be opened in.
| Mode |
Description |
| r |
Read Only mode, with the file pointer at the start of the file. |
| r+ |
Read/Write mode, with the file pointer at the start of the file. |
| w |
Write Only mode. Truncates the file (effectively overwriting it). If the file doesn't exist,
fopen will attempt to create the file. |
| w+ |
Read/Write mode. Truncates the file (effectively overwriting it). If the file doesn't exist,
fopen will attempt to create the file. |
| a |
Append mode, with the file pointer at the end of the file. If the file doesn't exist, fopen
will attempt to create the file. |
| a+ |
Read/Append, with the file pointer at the end of the file. If the file doesn't exist, fopen
will attempt to create the file. |
Note: The mode may also contain the letter 'b'. This is useful only on systems which differentiate between binary and text files (i.e.Windows. It's useless on Unix/Linux). If not needed, it will be
ignored.
Closing a File
The
fclose function is used to close a file when you are finished with it.
Reading from Files
You can read from files opened in r, r+, w+, and a+ mode. The
feof function is used to determine if the end of file is true.
if ( feof($fp) )
echo "End of file
";
The feof function can be used in a while loop, to read from the file until the end of file is encountered. A line at a time can be read with the
fgets function:
while( !feof($fp) ) {
// Reads one line at a time, up to 254 characters. Each line ends with a newline.
// If the length argument is omitted, PHP defaults to a length of 1024.
$myline = fgets($fp, 255);
echo $myline;
}
You can read in a single character at a time from a file using the
fgetc function:
while( !feof($fp) ) {
// Reads one character at a time from the file.
$ch = fgetc($fp);
echo $ch;
}
You can also read a single word at a time from a file using the
fscanf function. The function takes a variable number of parameters, but the first two parameters are mandatory. The first parameter is the file handle, the second parameter is a C-style format string. Any parameters passed after this are optional, but if used will contain the values of the format string.
if (!($fp = fopen($listFile, "r")))
exit("Unable to open $listFile.");
while (!feof($fp)) {
// Assign variables to optional arguments
$buffer = fscanf($fp, "%s %s %d", $name, $title, $age);
if ($buffer == 3) // $buffer contains the number of items it was able to assign
print "$name $title $age
\n";
}
Here is the file
list.txt:
Dave Programmer 34
Sue Designer 21
Lisa Programmer 29
Nigel User 19
You can also store the variables in an array by omitting the optional parameters in
fscanf:
while (!feof($fp)) {
$buffer = fscanf($fp, "%s %s %d"); // Assign variables to an array
// Use the list function to move the variables from the array into variables
list($name, $title, $age) = $buffer;
print "$name $title $age
\n";
}
You can read in an entire file with the
fread function. It reads a number of bytes from a file, up to the end of the file (whichever comes first). The
filesize function returns the size of the file in bytes, and can be used with the
fread function, as in the following example.
$listFile = "myfile.txt";
if (!($fp = fopen($listFile, "r")))
exit("Unable to open the input file, $listFile.");
$buffer = fread($fp, filesize($listFile));
echo "$buffer
\n";
fclose($fp);
You can also use the
file function to read the entire contents of a file into an array instead of opening the file with
fopen:
$array = file(‘filename.txt’);
Each array element contains one line from the file, where each line is terminated by a newline.
Writing to Files
The
fwrite function is used to write a string, or part of a string to a file. The function takes three parameters, the file handle, the string to write, and the number of bytes to write. If the number of bytes is omitted, the whole string is written to the file. If you want the lines to appear on separate lines in the file, use the \n character.
Note:
Windows requires a carriage return character as well as a new line character, so if you're using Windows, terminate the string with \r\n. The following
example logs the visitor to a file, then displays all the entries in the file.
\r\n";
else
$userDetails .= "
\r\n";
fwrite($fp, "$userDetails"); // Write the user details to the file
rewind($fp); // Move the file pointer to the start of the file
$entries = 0;
while(!feof($fp)) { // Display each line in the file
$buffer = fgets($fp, 1024);
if ($buffer != "") {
echo $buffer;
$entries++;
}
} // Show a summary
echo "There are $entries entries in the log file
";
fclose ($fp);
?>
Locking Files
boolean
flock ( resource fp, integer operation)
PHP supports a portable way of locking complete files in an advisory way (which means all accessing programs have to use the same way of locking or it will not work). If there is a possibility that more than one process could write to a file at the same time then the file should be locked.
flock() operates on
fp which must be an open file pointer.
operation is one of the following:
- To acquire a shared lock (reader), set operation to LOCK_SH
- To acquire an exclusive lock (writer), set operation to LOCK_EX
- To release a lock (shared or exclusive), set operation to LOCK_UN
- If you don't want flock() to block while locking, add LOCK_NB to LOCK_SH or LOCK_EX
When obtaining a lock, the process may block. That is, if the file is already locked, it will wait until it gets the lock to continue execution.
flock() allows you to perform a simple reader/writer model which can be used on virtually every platform (including most Unix derivatives and even Windows).
flock() returns
TRUE on success and
FALSE on error (e.g. when a lock could not be acquired).
Here is a script that writes to a log file with the
fputs function and then isplays the log file’s
contents:
”; // dump log
readfile(“/tmp/log.txt”);
echo “
\n”;
?>
Other Useful File Functions
The
opendir function returns a directory handle;
closedir closes a directory;
readdir reads a directory entry.
$myDirectory = opendir(“.”); // use the current directory
while($entryname = readdir($myDirectory)) {
echo “”;
echo “$entryname
”;
echo “”;
echo filesize($entryname); // the filesize function returns the file size in bytes
echo “
”;
echo “\n”;
}c
losedir($myDirectory);
The
is_dir function tests if a filename refers to a directory:
if(is_dir($filename))
echo $filename . “ is a directory”;
The
is_file function determines if a filename refers to a file:
if(is_file($filename))
echo $filename . “ is a file”;
The
is_readable function returns TRUE if the file exists and it is readable, otherwise it returns false. On Unix/Linux this is determined by the file’s permissions. On Windows, TRUE is always returned if the file exists.
if(is_readable($filename))
echo $filename . “ is readable”;
The
is_writable function determines whether the server will allow you to write data to the file before you attempt to open it:
if(is_writable(‘../quotes.txt’)) {
// attempt to open the file and write to it
} else {
echo ‘The file is not writable’;
}
Note:
there are many more file functions. Please refer to PHP documentation for an exhaustive list.
