I have a tool in PHP that I made to automate the process of generating some hex, which I then manually place in a file using a hex editor.
I have 1 byte which goes to offset 0x345, and a much larger section of varying length which goes to 0x560. I use Paste > Write so that the hex I generated replaces what is in it's way rather then increase the size of the file.
Is there a way I can automate this with fopen(); so that I can skip the manual pasting?
You can use these functions: fopen to open file, fseek to desired positions and fwrite your data.
Related
I need to split a big DBF file using php functions, this means that i have for example 1000 records, i have to create 2 files with 500 records each.
I do not have any dbase extension available nor i can install it so i have to work with basic php functions. Using basic fread function i'm able to correctly read and parse the file, but when i try to write a new dbf i have some problems.
As i have understood, the DBF file is structured in a 2 line file: the first line contains file info, header info and it's in binary. The second line contains the data and it's plain text. So i thought to simply write a new binary file replicating the first line and manually adding the first records in the first file, the other records in the other file.
That's the code i use to parse the file and it works nicely
$fdbf = fopen($_FILES['userfile']['tmp_name'],'r');
$fields = array();
$buf = fread($fdbf,32);
$header=unpack( "VRecordCount/vFirstRecord/vRecordLength", substr($buf,4,8));
$goon = true;
$unpackString='';
while ($goon && !feof($fdbf)) { // read fields:
$buf = fread($fdbf,32);
if (substr($buf,0,1)==chr(13)) {$goon=false;} // end of field list
else {
$field=unpack( "a11fieldname/A1fieldtype/Voffset/Cfieldlen/Cfielddec", substr($buf,0,18));
$unpackString.="A$field[fieldlen]$field[fieldname]/";
array_push($fields, $field);
}
}
fseek($fdbf, 0);
$first_line = fread($fdbf, $header['FirstRecord']+1);
fseek($fdbf, $header['FirstRecord']+1); // move back to the start of the first record (after the field definitions)
first_line is the variable the contains the header data, but when i try to write it in a new file something wrong happens and the row isn't written exactly as it was read. That's the code i use for writing:
$handle_log = fopen($new_filename, "wb");
fwrite($handle_log, $first_line, strlen($first_line) );
fwrite($handle_log, $string );
fclose($handle_log);
I've tried to add the b value to fopen mode parameter as suggested to open it in a binary way, i've also taken a suggestion to add exactly the length of the string to avoid the stripes of some characters but unsuccessfully since all the files written are not correctly in DBF format. What can i do to achieve my goal?
As i have understood, the DBF file is structured in a 2 line file: the
first line contains file info, header info and it's in binary. The
second line contains the data and it's plain text.
Well, it's a bit more complicated than that.
See here for a full description of the dbf file format.
So it would be best if you could use a library to read and write the dbf files.
If you really need to do this yourself, here are the most important parts:
Dbf is a binary file format, so you have to read and write it as binary. For example the number of records is stored in a 32 bit integer, which can contain zero bytes.
You can't use string functions on that binary data. For example strlen() will scan the data up to the first null byte, which is present in that 32 bit integer, and will return the wrong value.
If you split the file (the records), you'll have to adjust the record count in the header.
When splitting the records keep in mind that each record is preceded by an extra byte, a space 0x20 if the record is not deleted, an asterisk 0x2A if the record is deleted. (for example, if you have 4 fields of 10 bytes, the length of each record will be 41) - that value is also available in the header: bytes 10-11 - 16-bit number - Number of bytes in the record. (Least significant byte first)
The file could end with the end-of-file marker 0x1A, so you'll have to check for that as well.
I'm trying to use PHP to parse a custom gzip archive file format that was created in Delphi (not my code!). The format is basically:
4-byte integer: count of files in archive
for each compressed file:
4-byte integer: filename length [n]
[n] bytes: filename
4-byte integer: uncompressed file length [m]
[????] bytes: gzipped content
I can read the file and actually decode the first compressed file correctly by using zlib_decode() with a max uncompressed length of [m] bytes on the remainder of the file after I know the length ([m]), but then I'm stuck because I don't know how far into the substring I should go to find the next filename -- zlib_decode() doesn't return the number of compressed bytes that it processed before stopping. Since this is a custom format, it doesn't seem like I can use the normal gzopen()/gzread() functions because the entire file isn't compressed (I tried, it doesn't work).
This code works in Delphi because apparently you can pass a file handle back and forth between normal file reading functions and the System.ZLib decoding functions -- you can read [m] uncompressed bytes and the pointer will remain at the last compressed byte -- but PHP doesn't seem to support switching between read-as-normal and read-as-gzip on the fly that way.
Am I missing an obvious way in PHP to deal with a mixed-content file format like this, where metadata and compressed data are stacked together this way? Or am I out of luck without knowing the compressed data length?
A dirty workaround is to recompress the content of each file as I am able to parse it, use that to calculate the compressed length, and adjust the file pointer in the original file manually as follows:
$current_pos = ftell($handle);
$skip_length = strlen(gzencode($uncompressed_text,9,FORCE_DEFLATE));
fseek($handle, $skip_length+$current_pos);
This works, but feels very hack-ish. I'd still be open to any better approaches.
EDIT:
Just a note that this eventually failed. However, I was fortunate enough to know in advance the list of expected filenames and I was able to do the following (more reliable since zlib_decode() will decode as much as it can and discard the rest anyway):
foreach ($filenames as $thisFilename) {
$thisPos = strpos($rawData, $thisFilename);
$gzresult = zlib_decode(substr($rawData, $thisPos + strlen($table) + 8)); // skip 8 bytes for filename size and uncompressed data size, which are useless info.
}
I'm looking to read contents of a file between two tags in a large text file (so can't read the whole file at once due to memory restrictions on my server provider). This file has around 500000 lines of text.
This ( PHP: Read Specific Line From File ) isn't an option (I don't think), as the text I need to read varies in length and will take up multiple lines (varies from 20-5000 lines).
I am planning to use fopen, fread (read only) and fclose to read the file contents. I have experience of using these functions already.
I am looking to read all the contents in a selected part of the file. i.e.
File contents example
<<TAGNAME-1>>AAAA AAAA AAAA<<//TAGNAME-1>>
<<TAGNAME-2>>TEXT TEXT TEXT<<//TAGNAME-2>>
To select the text "AAAA AAAA AAAA" between the <<TAGNAME-1>> and <<//TAGNAME-1>> when TAGNAME-1 is called as a variable in my script.
How could I go about selecting all the text between the two tags that I require? (and ignore the remainder of the file) I have the ability to create the two tags where required in my php script - my issue is implementing this within the fread function.
You could grep the text file which would only return the text with a matching tag.
$tagnum = 2; //variable
$pattern = "<<TAGNAME-";
$searchstr = $pattern.$tagnum; //concat the prefix with the tag number
$fpath ="testtext.txt"; //define path to text file
$result = exec('grep -in "'.$searchstr.'" '.$fpath);
echo $result;
Where $tagnum would define each tag to search. I've tested it in my sandbox and it works as expected. Note this will read the whole line until the end tad or newline is reached.
Regards,
I am trying to write a text at a specific position in a file that already has some content. After writing I find the file truncated to the size of the text plus fseek position and the first characters with value 0. Is this the normal behaviour or am I missing something? I want to mention that I'm trying to avoid loading the file into memory and writing it back.
$file = fopen("text.txt","w");
fseek($file,3);
fwrite($file,"Hello");
fclose($file);
You need to open the file in c mode, else it's truncated on fopen:
$file = fopen("text.txt","c");
See http://php.net/manual/de/function.fopen.php for a documentation of all file open modes and what exactly they do. Also see the http://www.php.net/manual/en/function.fseek.php manual
Yes this is normal behaviour :
fopen($file, "w"):
place the file pointer at the beginning of the file and truncate the file to zero length.
fseek():
In general, it is allowed to seek past the end-of-file; if data is then written, reads in any unwritten region between the end-of-file and the sought position will yield bytes with value 0. [..]
If you have opened the file in append (a or a+) mode, any data you write to the file will always be appended, regardless of the file position, and the result of calling fseek() will be undefined.
You probably want to open the file in a non truncating write mode (e.g. "c" but not "a").
i need vb.net equivlants of php fopen, fseek, and fwrite... also, i need to read and write data, not just text. I need to write data at specific byte position to x amount of bytes, as well as read at byte position to x amount of bytes...
Yes look at the System.IO.File class.
use the 'Open' method to get a FileStream. This has the functions your looking for i.e. seek,read,write
http://msdn.microsoft.com/en-US/library/system.io.file_members(v=vs.80).aspx
http://msdn.microsoft.com/en-US/library/system.io.filestream.write(v=vs.80).aspx