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How can I use PHP to update record in flat file

Posted on 2008-06-16
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Last Modified: 2012-05-05
I have a flat file/PHP based poll system.  Using a database is out of the question on the server it is on.

So far, I have it working except for updating a row with the new results.  I can write to the file, I just don't know how to replace just that one row.

My text file is:
Poll ID||Question||Yes Votes||No Votes
107||Do you like this so far?||3||2
108||Do you like this so far?||3||2
109||Do you like this so far?||3||2
110||Do you like this so far?||3||2
111||Do you like this so far?||3||2
112||Do you like this so far?||3||2
113||Do you like this so far?||3||2
poll-vote.php.txt
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Question by:baumli1
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7 Comments
 
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Accepted Solution

by:
glcummins earned 336 total points
ID: 21797682
Here is one possible solution. In this case, you read the entire contents of the file into an array, search the array for a specific value of Poll ID. If the value matches, update the string.


<?php
 
// Change this filename as necessary
$filename = "flatfile.txt";
$fh = fopen($filename, 'r');
 
$contents = fread($fh, filesize($filename));
 
fclose($fh);
 
// If you are on a Windows server, change "\n" to "\r\n"
$arrLines = explode("\n", $contents);
 
foreach ($arrLines as $key=>$line)
{
	$arrTemp = explode('||', $line);
	if ($arrTemp[0] == '111')
	{
		$arrTemp[1] = 'This is the new value';
		$outputString = implode('||', $arrTemp);
		$arrLines[$key] = $outputString;
	}
}
 
// If you are on a Windows server, change "\n" to "\r\n"
$outputContents = implode("\n", $arrLines);
 
// You will probably want to write to the same file as before, rather than to a new file.
// Change this line as necessary
$fh = fopen('flatfile2.txt', 'w');
fwrite($fh, $outputContents);
fclose($fh);
 
?>

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LVL 17

Expert Comment

by:jasonsbytes
ID: 21797688
what you need to do is write the entire file to a temporary file with your changes, then move the temp file back to the original file.

There is no way to modify just a line in a file using php.

Make sense?
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Author Comment

by:baumli1
ID: 21797878
I've almost got it I think.  I store all the contents in an array anyways.  So after I'm done with all the processing, I can write the array back out to the flat file.  The only problem now is that it just appends the array to the end of the flat file.  Is there a way to empty out the file first, or just overwrite the contents with the new array?
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LVL 24

Expert Comment

by:glcummins
ID: 21797899
To truncate the file, when you open the file the second time for writing, use:

 fopen($filename, 'w');

The 'w' says:

 "Open for writing only; place the file pointer at the beginning of the file and truncate the file to zero length. If the file does not exist, attempt to create it." (http://www.php.net/manual/en/function.fopen.php)
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Author Comment

by:baumli1
ID: 21797970
I actually never closed the file before writing to it again, so I used an "r+" when I first opened it.  And that did the trick.

The only think I worry about it keeping the results file open, while other people may be accessing it.
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LVL 17

Assisted Solution

by:jasonsbytes
jasonsbytes earned 332 total points
ID: 21798018
after you open it and load it into an array, close it...

then write the new data to a temp file...
then move the temp file back to the original...

moving is faster than writing and should prevent someone from opening it while it's being written to.
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LVL 1

Assisted Solution

by:kumarakam
kumarakam earned 332 total points
ID: 21798042
Here is a sample that can search and replace as many text in one step. It reads a from one file and writes to another file.


<?php
$infile = "$myfilein";
$outfile = "$myfileout";
 
$patterns[0] = "first old text to be replaced";
$replacements[0] = "first new text to replace";
 
$patterns[1] = "second old text to be replaced";
$replacements[1] = "second new text to replace";
 
$oldcontent = file_get_contents($infile);
$newcontent = preg_replace($patterns, $replacements, $oldcontent);
$data = file_put_contents($outfile,$newcontent);
?>

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