This is my code:
$zplHandle = fopen($target_file,'w');
fwrite($zplHandle, $zplBlock01);
fwrite($zplHandle, $zplBlock02);
fwrite($zplHandle, $zplBlock03);
fclose($zplHandle);
When will the file be saved? Is it immediately after writing to it or after closing it?
I am asking this because I have Printfil listening to files in a folder and prints any file that is newly created. If PHP commits a save immediately after fwrite, I may run into issues of Printfil not capturing the subsequent writes.
Thank you for the help.
PHP may or may not write the content immediately. There is a caching layer in between. You can force it to write using fflush(), but you can't force it to wait unless you use only one fwrite().
I made a tiny piece of code to test it and it seems that after fwrite the new content will be detected immediately,not after fclose.
Here's my test on Linux.
#!/usr/bin/env php
<?php
$f = fopen("file.txt","a+");
for($i=0;$i<10;$i++)
{
sleep(1);
fwrite($f,"something\n");
echo $i," write ...\n";
}
fclose($f);
echo "stop write";
?>
After running the PHP script ,I use tail -f file.txt to detect the new content.And It shows new contents the same time as php's output tag.
the file will be saved on fclose. if you want to put the content to the file before, use fflush().
Assuming your working in PHP 5.x, try file_put_contents() instead, as it wraps the open/write/close into one call.
http://us3.php.net/manual/en/function.file-put-contents.php
Related
actual I finished writing my program. Because it is only a plugin and it runs on a external server I still want to see if I get some errors or something else in the console.
I wrote every console input with echo ...;. My question now is if it is possible to get the text of the console?
Because then I could easily safe it in a .txt file and could get access to it from the web :) - Or is there another way to get the console text?
I could probably just say fwrite(...) instand of echo ...;. But this will cost a lot of time...
Greetings and Thank You!
An alternative that could be usefull on windows would be to save all the output buffer to a txt, first check your php configuration for the console app implicit_flush must be off then
<?php
ob_start(); //before any echo
/** YOUR CODE HERE **/
$output = ob_get_contents(); //this variable has all the echoes
file_put_contents('c:\whatever.txt',$output);
ob_flush(); //shows the echoes on console
?>
If your goal is to create a text file to access, then you should create a text file directly.
(do this instead of echoing to console)
$output = $consoleData . "\n";
$output .= $moreConsoleData . "\n";
(Once you've completed that, just create the file:)
$file = fopen('output.txt', 'a');
fwrite($file, $output);
fclose($file);
Of course, this is sparse - you should also check that the file exists, create it if necessary, etc.
For console (commando line interface) you can redirect the output of your script:
php yourscript.php > path-of-your-file.txt
If you haven't access to a command line interface or to edit the cronjob line, you can duplicate the starndar output at the begining of the script:
$fdout = fopen('path-to-your-script.txt', 'wb');
eio_dup2($fdout, STDOUT);
eio_event_loop();
fclose($fdout);
(eio is an pecl extension)
If you are running the script using the console (i.e. php yourscript.php), you can easily save the output my modifying your command to:
php yourscript.php > path/to/log.txt
The above command will capture all output by the script and save it to log.txt. Change the paths for your script / log as required.
I am trying to understand the right way to synchronize file read/write using the flock in PHP.
I have two php scripts.
testread.php:
<?
$fp=fopen("test.txt","r");
if (!flock($fp,LOCK_SH))
echo "failed to lock\n";
else
echo "lock ok\n";
while(true) sleep(1000);
?>
and testwrite.php:
<?
$fp=fopen("test.txt","w");
if (flock($fp,LOCK_EX|LOCK_NB))
{
echo "acquired write lock\n";
}
else
{
echo "failed to acquire write lock\n";
}
fclose($fp);
?>
Now I run testread.php and let it hang there. Then I run testwrite.php in another session. As expected, flock failed in testwrite.php. However, the content of the file test.txt is cleared when testwrite.php exits. The fact is, fopen always succeeds even if the file has been locked in another process. If the file is opened with "w" mode, the file content will be erased regardless of the lock. So what is the point of flock here? It doesn't really protect anything.
You are using fopen() with the w mode in testwrite.php. When using the w option fopen() will truncate the file after opening it. (see fopen()).
Because of that the file gets truncated in your example before you try to obtain the exclusive lock. However you'll need an open file descriptor in order to use flock().
The way out of this dilemma is to use a lock file different from the file you are working on. The flock() manual page mentions this:
Because flock() requires a file pointer, you may have to use a special lock file to protect access to a file that you intend to truncate by opening it in write mode (with a "w" or "w+" argument to fopen()).
The accepted answer is overly complicated. You can simply open the file using a "c" argument, which doesn't truncate the file. Then call ftruncate() only if you acquire the lock.
From the documentation:
'c' Open the file for writing only. If the file does not exist, it is
created. If it exists, it is neither truncated (as opposed to 'w'),
nor the call to this function fails (as is the case with 'x'). The
file pointer is positioned on the beginning of the file. This may be
useful if it's desired to get an advisory lock (see flock()) before
attempting to modify the file, as using 'w' could truncate the file
before the lock was obtained (if truncation is desired, ftruncate()
can be used after the lock is requested).
Let's say that we have a program X that continuously write a file for example the /tmp/test.file
I have a script in PHP that serves this file to the client so that he can download/read it.
How i'm able to do this continuously as the data are being written in the /tmp/test.file?
If i use the below code
<?php
$fp = fopen("/tmp/test.file","r");
while(!feof($fp))
{
echo fread($fp,4096);
}
fclose($fp);
It instantly stops because it reads the whole file until EOF so it doesnt care if another process is writing at this file.
Thank you
As a suggestion, use a continues Ajax call (for example 5 seconds interval) to the PHP script file, and get the file content via offset. You can store the current offset of file into SESSION or COOKIE.
You can get file offset by using PHP's ftell function.
As PHP's official document defines ftell():
ftell — Returns the current position of the file read/write pointer
Also, stream_get_contents() function might be useful as PHP's official document defines it:
stream_get_contents — Reads remainder of a stream into a string
then, In each interval, append the response data to a HTML tag.
Have a file in a website. A PHP script modifies it like this:
$contents = file_get_contents("MyFile");
// ** Modify $contents **
// Now rewrite:
$file = fopen("MyFile","w+");
fwrite($file, $contents);
fclose($file);
The modification is pretty simple. It grabs the file's contents and adds a few lines. Then it overwrites the file.
I am aware that PHP has a function for appending contents to a file rather than overwriting it all over again. However, I want to keep using this method since I'll probably change the modification algorithm in the future (so appending may not be enough).
Anyway, I was testing this out, making like 100 requests. Each time I call the script, I add a new line to the file:
First call:
First!
Second call:
First!
Second!
Third call:
First!
Second!
Third!
Pretty cool. But then:
Fourth call:
Fourth!
Fifth call:
Fourth!
Fifth!
As you can see, the first, second and third lines simply disappeared.
I've determined that the problem isn't the contents string modification algorithm (I've tested it separately). Something is messed up either when reading or writing the file.
I think it is very likely that the issue is when the file's contents are read: if $contents, for some odd reason, is empty, then the behavior shown above makes sense.
I'm no expert with PHP, but perhaps the fact that I performed 100 calls almost simultaneously caused this issue. What if there are two processes, and one is writing the file while the other is reading it?
What is the recommended approach for this issue? How should I manage file modifications when several processes could be writing/reading the same file?
What you need to do is use flock() (file lock)
What I think is happening is your script is grabbing the file while the previous script is still writing to it. Since the file is still being written to, it doesn't exist at the moment when PHP grabs it, so php gets an empty string, and once the later processes is done it overwrites the previous file.
The solution is to have the script usleep() for a few milliseconds when the file is locked and then try again. Just be sure to put a limit on how many times your script can try.
NOTICE:
If another PHP script or application accesses the file, it may not necessarily use/check for file locks. This is because file locks are often seen as an optional extra, since in most cases they aren't needed.
So the issue is parallel accesses to the same file, while one is writing to the file another instance is reading before the file has been updated.
PHP luckily has a mechanisms for locking the file so no one can read from it until the lock is released and the file has been updated.
flock()
can be used and the documentation is here
You need to create a lock, so that any concurrent requests will have to wait their turn. This can be done using the flock() function. You will have to use fopen(), as opposed to file_get_contents(), but it should not be a problem:
$file = 'file.txt';
$fh = fopen($file, 'r+');
if (flock($fh, LOCK_EX)) { // Get an exclusive lock
$data = fread($fh, filesize($file)); // Get the contents of file
// Do something with data here...
ftruncate($fh, 0); // Empty the file
fwrite($fh, $newData); // Write new data to file
fclose($fh); // Close handle and release lock
} else {
die('Unable to get a lock on file: '.$file);
}
I experimenting with twitter streaming API,
I use Phirehose to connect to twitter and fetch the data but having problems storing it in files for further processing.
Basically what I want to do is to create a file named
date("YmdH")."."txt"
for every hour of connection.
Here is how my code looks like right now (not handling the hourly change of files)
public function enqueueStatus($status)
$data = json_decode($status,true);
if(isset($data['text'])/*more conditions here*/) {
$fp = fopen("/tmp/$time.txt");
fwirte ($status,$fp);
fclose($fp);
}
Help is as always much appreciated :)
You want the 'append' mode in fopen - this will either append to a file or create it.
if(isset($data['text'])/*more conditions here*/) {
$fp = fopen("/tmp/" . date("YmdH") . ".txt", "a");
fwrite ($status,$fp);
fclose($fp);
}
From the Phirehose googlecode wiki:
As of Phirehose version 0.2.2 there is
an example of a simple "ghetto queue"
included in the tarball (see file:
ghetto-queue-collect.php and
ghetto-queue-consume.php) that shows
how statuses could be easily collected
on to the filesystem for processing
and then picked up by a separate
process (consume).
This is a complete working sample of doing what you want to do. The rotation time interval is configurable too. Additionally there's another script to consume and process the written files too.
Now if only I could find a way to stop the whole sript, my log keeps filling up (the script continues execution) even if I close the browser tab :P