Read the file into memory, make the changes, and rewrite the file. Open the file with mode r+ (rb+, if necessary, on Windows) and adjust its length with ftruncate( ) after writing out changes:
// open the file for reading and writing $fh = fopen('pickles.txt','r+') or die($php_errormsg); // read the entire file into $s $s = fread($fh,filesize('pickles.txt')) or die($php_errormsg); // ... modify $s ... // seek back to the beginning of the file and write the new $s rewind($fh); if (-1 == fwrite($fh,$s)) { die($php_errormsg); } // adjust the file's length to just what's been written ftruncate($fh,ftell($fh)) or die($php_errormsg); // close the file fclose($fh) or die($php_errormsg);
The following code turns text emphasized with asterisks or slashes into text with HTML <b> or <i> tags:
$fh = fopen('message.txt','r+') or die($php_errormsg); // read the entire file into $s $s = fread($fh,filesize('message.txt')) or die($php_errormsg); // convert *word* to <b>word</b> $s = preg_replace('@\*(.*?)\*@i','<b>$1</b>',$s); // convert /word/ to <i>word</i> $s = preg_replace('@/(.*?)/@i','<i>$1</i>',$s); rewind($fh); if (-1 == fwrite($fh,$s)) { die($php_errormsg); } ftruncate($fh,ftell($fh)) or die($php_errormsg); fclose($fh) or die($php_errormsg);
Because adding HTML tags makes the file grow, the entire file has to be read into memory and then processed. If the changes to a file make each line shrink (or stay the same size), the file can be processed line by line, saving memory. This example converts text marked with <b> and <i> to text marked with asterisks and slashes:
$fh = fopen('message.txt','r+') or die($php_errormsg); // figure out how many bytes to read $bytes_to_read = filesize('message.txt'); // initialize variables that hold file positions $next_read = $last_write = 0; // keep going while there are still bytes to read while ($next_read < $bytes_to_read) { /* move to the position of the next read, read a line, and save * the position of the next read */ fseek($fh,$next_read); $s = fgets($fh,1048576) or die($php_errormsg); $next_read = ftell($fh); // convert <b>word</b> to *word* $s = preg_replace('@<b[^>]*>(.*?)</b>@i','*$1*',$s); // convert <i>word</i> to /word/ $s = preg_replace('@<i[^>]*>(.*?)</i>@i','/$1/',$s); /* move to the position where the last write ended, write the * converted line, and save the position for the next write */ fseek($fh,$last_write); if (-1 == fwrite($fh,$s)) { die($php_errormsg); } $last_write = ftell($fh); } // truncate the file length to what we've already written ftruncate($fh,$last_write) or die($php_errormsg); // close the file fclose($fh) or die($php_errormsg);
Section 11.10 and Section 11.11 for additional information on converting between ASCII and HTML; Section 18.15 discusses fseek( ) and rewind( ) in more detail; documentation on fseek( ) at http://www.php.net/fseek, rewind( ) at http://www.php.net/rewind, and ftruncate( ) at http://www.php.net/ftruncate.
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