popen in PHP

popen — Opens process file pointer
Syntax:

resource popen ( string $command , string $mode )
Opens a pipe to a process executed by forking the command given by command.

Parameters:

command
The command

mode
The mode

Return values: Returns a file pointer identical to that returned by fopen(), except that it is unidirectional (may only be used for reading or writing) and must be closed with pclose(). This pointer may be used with fgets(), fgetss(), and fwrite(). When the mode is 'r', the returned file pointer equals to the STDOUT of the command, when the mode is 'w', the returned file pointer equals to the STDIN of the command.

If an error occurs, returns FALSE.



Example #1 popen() example

<?php
$handle = popen("/bin/ls", "r");
?>
If the command to be executed could not be found, a valid resource is returned. This may seem odd, but makes sense; it allows you to access any error message returned by the shell:

Example #2 popen() example

<?php
error_reporting(E_ALL);

/* Add redirection so we can get stderr. */
$handle = popen('/path/to/executable 2>&1', 'r');
echo "'$handle'; " . gettype($handle) . "\n";
$read = fread($handle, 2096);
echo $read;
pclose($handle);
?>


Note:
If you're looking for bi-directional support (two-way), use proc_open().
Note: When safe mode is enabled, you can only execute files within the safe_mode_exec_dir. For practical reasons, it is currently not allowed to have .. components in the path to the executable.
Warning
With safe mode enabled, the command string is escaped with escapeshellcmd(). Thus, echo y | echo x becomes echo y \| echo x.

ftell in PHP

ftell — Returns the current position of the file read/write pointer
Syntax:

int ftell ( resource $handle )
Returns the position of the file pointer referenced by handle.

Parameters:

handle
The file pointer must be valid, and must point to a file successfully opened by fopen() or popen(). ftell() gives undefined results for append-only streams (opened with "a" flag).

Return values: Returns the position of the file pointer referenced by handle as an integer; i.e., its offset into the file stream.

If an error occurs, returns FALSE.

Note: Because PHP's integer type is signed and many platforms use 32bit integers, some filesystem functions may return unexpected results for files which are larger than 2GB.


Example #1 ftell() example

<?php

// opens a file and read some data
$fp = fopen("/etc/passwd", "r");
$data = fgets($fp, 12);

// where are we ?
echo ftell($fp); // 11

fclose($fp);

?>

fgets in PHP

fgets — Gets line from file pointer
Syntax:

string fgets ( resource $handle [, int $length ] )
Gets a line from file pointer.

Parameters:

handle
The file pointer must be valid, and must point to a file successfully opened by fopen() or fsockopen() (and not yet closed by fclose()).

length
Reading ends when length - 1 bytes have been read, or a newline (which is included in the return value), or an EOF (whichever comes first). If no length is specified, it will keep reading from the stream until it reaches the end of the line.

Note:
Until PHP 4.3.0, omitting it would assume 1024 as the line length. If the majority of the lines in the file are all larger than 8KB, it is more resource efficient for your script to specify the maximum line length.
Return values: Returns a string of up to length - 1 bytes read from the file pointed to by handle. If there is no more data to read in the file pointer, then FALSE is returned.

If an error occurs, FALSE is returned.

Changelog

Version Description
4.3.0 fgets() is now binary safe


Example #1 Reading a file line by line

<?php
$handle = @fopen("/tmp/inputfile.txt", "r");
if ($handle) {
    while (($buffer = fgets($handle, 4096)) !== false) {
        echo $buffer;
    }
    if (!feof($handle)) {
        echo "Error: unexpected fgets() fail\n";
    }
    fclose($handle);
}
?>


Note: If PHP is not properly recognizing the line endings when reading files either on or created by a Macintosh computer, enabling the auto_detect_line_endings run-time configuration option may help resolve the problem.
Note:
People used to the 'C' semantics of fgets() should note the difference in how EOF is returned.