my friends
I have a question about why file extensions are created?
I found a quote on Wikipedia
"They are commonly used to imply information about the way data might be stored in the file"
what does it mean?
File extension is an identifier which tell the operating system what kind of data and file type they are working with and what associated program opens the file.
if u have an .apk extension file, system can easily recognize it as an application file. If it is an mp4, means it's some kind of multimedia file and can be operated with multimedia applications.
They are commonly used to imply information about the way data might be stored in the file. A normal text editor uses .txt as extension when an html uses extension .html These two files stores data differently.
Related
I am working on a web app project to block all the file executable from file upload.
Example: user can upload, txt, png, image and video files and not any executable scripts like, Perl, Python, exe, PHP, .so, .sh files.
If it is a PHP file, then I strstr for "<?php" tag, If this tag is present, then it is PHP file. How can we find the same for other script/executable files?
Edit: Some time hackers will upload the malicious files using .png or .jpg extn, so what is the pattern to check inside the files?
Rather than making your own checks you make use of an existing library and you block everything that does not register as a desired format.
Most such libraries guess the content type and encoding of a file by looking for certain signatures or magic byte sequences at specific positions within the file.
Other libraries may be more specialised and will for example only identify image or video formats.
https://www.php.net/manual/en/intro.fileinfo.php
https://github.com/ahupp/python-magic
https://docs.python.org/3/library/imghdr.html
The file programme is a command line tool for identification of file types.
After the first pass where you identify and accept only the desired file formats you should then make all files that are not rejected go through an antivirus scanner.
Depending on you use cases you may decide to strip the original file name extension and/or even the complete file name that was provided during the upload and assign the mime-type that was detected rather than rely on user provided properties.
I have a piece of metadata that I would like to hide in a plain text file, won't be shown by generic text editor, is there a way to do that?
Not within the file itself. For storing metadata I suggest using alternative data streams in the filesystem. In OS X (with HFS) they're called Forks and in Windows (with NTFS) they're called Alternate Data Streams. You're probably already familiar with the "Resource fork" on OS X.
...basically it's a hidden file with the same name as the original file (and moves with it), except it's accessed with special (normally illegal) characters in the file path.
Note that ADS files are not moved/copied between incompatible filesystems (e.g. from NTFS to FAT), when compressed into a zip or archived into a tarball, nor when uploaded, so never assume that your ADS file will be persistent (making it useful for storing local-machine-only metadata, such as editor preferences, etc)
On Windows, you can learn more here: http://support.microsoft.com/kb/105763
On Mac OS X, you can learn more here: https://developer.apple.com/library/mac/documentation/Carbon/Reference/File_Manager/DeprecationAppendix/AppendixADeprecatedAPI.html#//apple_ref/c/func/FSAllocateFork
On Linux, the main filesystems (extfs: ext3, ext4, etc) do not support forks in the filesystem. When reading a HFS volume on Linux you access forks by appending the fork name to the filename (e.g. "/foo/bar/rsrc" to access the resource fork of the file "/foo/bar").
I have built an Excel/VBA tool to validate csv files to ensure the data they contain is valid. They csv can come originate from anywhere (from a full blown unix system or a desktop user saving data out from Excel). The Excel tool is sent out to businesses so they can validate their csv files in their own environment and without taking the risk of their data leaving thier systems. Thus, the solution needs to be in native VBA and not link into external libraries.
So using VBA, I need to be able to automatically detect UTF-8 (with or without BOM) or ANSI file encodings and warn the user if these are not the file encodings used for the csv.
I think this would perhaps involve reading in a few bytes from the start of the file and determining the encoding based on the existance of the byte order mark.
Could you help me get me started on the right track?
Assuming you have the freedom to ask user to choose the correct file type, making them responsible for what they choose as a file ;)
That means, you can create a form where users can choose the filename and the encoding type like how we do on file open wizard.
Else,
I suggest you to use the FileSystemObject. It returns a TextStream which can be utilized to determine the encoding. I doubt VBA supports other types of encoding and please correct me if it does :) and happy to hear. :)
how to detect encoding type
msdn object library model
Here is a link for further considerations:-
change encode type
All I need is to show .doc files in qt application on Linux. No need edit/save or something else.
Is it possible?
Of course it's possible. But the file reading, parsing, and displaying would really be carried out by the underlying language, not Qt. So, if you think about it, C++ and Python and whatever else is quite capable of parsing and displaying what is essentially a text file (or for .dox an XML file).
The implementation details of how to go about that are quite another matter. You have to contend with a huge portion of the file that is merely there to render the file's styling, etc.
I use various 3rd party libraries to convert files on my Linux server. For instance, ImageMagick/convert for images, libreoffice3.5/convert-to for Microsoft Office documents, etc.
Is it possible that these applications require the pre-converted file to have the proper extension for the type of file? For instance, if the file was a png file, it would need to be called whatever.png and not just whatever.
Thank you
your question sounds general, and in general linux apps do not require extensions. bash will execute a .png file with shell commands happily and vi will open a text file called a.exe. extensions are in general not a unix/linux concept to begin with and . is just an allowed character in the file name.
this being said, some particular application may interpret or even require correct extensions.