I have run into a problem in one of my Tcl scripts where I am uploading a file from a Windows computer to a Unix server. I would like to get just the original file name from the Windows file and save the new file with the same name. The problem is that [file tail windows_file_name] does not work, it returns the whole file name like "c:\temp\dog.jpg" instead of just "dog.jpg". File tail works correctly on a Unix file name "/usr/tmp/dog.jpg", so for some reason it is not detecting that the file is in Windows format. However Tcl on my Windows computer works correctly for either name format. I am using Tcl 8.4.18, so maybe it is too old? Is there another trick to get it to split correctly?
Thanks
The problem here is that on Windows, both \ and / are valid path separators so long Windows API is concerned (even though only \ is deemed to be "official" on Windows). On the other hand, in POSIX, the only valid path separator is /, and the only two bytes which can't appear in a pathname component are / and \0 (a byte with value 0).
Hence, on a POSIX system, "C:\foo\bar.baz" is a perfectly valid short filename, and running
file normalize {C:\foo\bar.baz}
would yield /path/to/current/dir/C:\foo\bar.baz. By the same logic, [file tail $short_filename] is the same as $short_filename.
The solution is to either do what Glenn Jackman proposed or to somehow pass the short name from the browser via some other means (some JS bound to an appropriate file entry?). Also you could attempt to detect the user's OS from the User-Agent header.
To make Glenn's idea more agnostic to user's platform, you could go like this:
Scan the file name for "/".
If none found, do set fname [string map {\\ /} $fname] then go to the next step.
Use [file tail $fn] to extract the tail name.
It's not very bullet-proof, but supposedly better than nothing.
You could always do [lindex [split $windows_file_name \\] end]
Related
For example: '">sometext<.txt
I am currently trying to save a file in that form, so If I upload the file on a website I'm hopping to find the XSS bug.
Windows (but not necessarily NTFS) prohibits the following characters in filenames: \/:*?"<>|, which precludes the characters necessary for most XSS attacks (<>"). Windows also disallows reserved DOS device file-names like COM, NUL, etc (though it is possible to create a file with that name, it cannot be done using the normal Win32 filesystem API).
Linux (and UNIX and POSIX in general) is more permissive: every character is allowed in a filename except for / (the directory separator character) and \0 (NULL, a raw zero).
I imagine an insecure web-application that saves uploaded files with their filenames intact and without having sanitized filenames probably will succumb to an XSS attack - unless they're also careful to never render HTML raw.
Windows prohibits these characters. But you could try Azure Blob Storage
Python 3+
This is the error i get
This is my code
I want the user to input some words, then the program should run each word through my two textfiles, if the word exists in any of them, I want the program to add +1 to the positive/negative count list.
Thank you for your help :)
Seems like you have stumbled upon a Decoding error when trying to open one of the input files in the wordlist function. it is usually hard to determine the encoding used for a particular file. so you could :
1.Try opening the file with a different encoding such as ISO-8859-15,etc.
def OpenFile():
try:
with open("My File.txt",mode="r",encoding="IS0-8859-15")
#do process My File
except UnicodeDecodeError:
print("Something went Wrong Try a different file encoding")
else:
#everything was okay, return the required
finally:
# clean up here
2. Look it modules that try and determine the correct encoding for the file such as the chardet module
Install the
chardet module :
sudo pip3 install chardet
you can run it at the command line with your file as the Argument to determine the encoding
cd /path/to/File/
chardetect My\ File.txt
this should return the likely encoding for the given file
3.You can use the chardet module inside your python code however this is recommended in a case where you will be opening a file you do not have access to e.g at a clients computer whom wants to open another specified file
and reopening the same file and redetecting the encoding will cause your program to be slow.
First of all positive_count and negative_count should be integers and not lists. If you wish to count, adding 1 to the list isn't really what you're trying to accomplish.
Second of all, the UnicodeDecodeError is there because the encoding of the underlying file is not utf-8. Did you try utf-16 or utf-16-le? In case you're using Windows, utf-16-le is probably the encoding used unless you're using code-points in which case guessing will be a nightmare.
As a general question: What's the role of file extension when determining file types?
For example, I can change .jpeg file to .png extension and even .txt. Of course, in the case of changing to .txt, it will neither be opened as picture, nor readable.
To determine file type, it seems the safe way is to parse the first few bytes of the file. If extension is not trustable, extension is no more than file name.
As a general rule, you should ALWAYS parse the COMPLETE file in order to be sure that the file is what the extension says. As you can easily imagine, it is pretty simple to create a binary file resembling a e.g. BMP (with a correct header) but then containing something different.
You should never trust the extension neither the header because otherwise a malicious user could exploit some of your code to generate e.g. a buffer overflow, and this is absolutely paramount if you are writing programs that must run at root/admin privilege.
Having said the obvious, the file extension nowadays is mainly used so that the OS can associate a program to that particular file (usually calling the program and passing the selected file as first parameter), and then it's up to the program to determine the file content.
It is a little bit different when talking about executable files. Under Unix, in order to be executable a file has to have the "x" flag set, otherwise it would not run, regardless of the extension. Under Windows, there is not such thing and the OS relies on only a few extensions (EXE, COM, BAT, etc.) to determine which files can be executed.
The EXE file, for example, has to start with "MZ" followed by some information for its allocation and size (http://www.delorie.com/djgpp/doc/exe/) and the OS surely checks its internal headers. Other formats (e.g. the COM executable format of the MS-DOS era) is just "pure" assembly code, so there is no check done by the OS. It just interprets those opcodes, hoping that everything will be fine.
So, to summarize:
File extension is mainly used so that the OS can call the appropriate program to open it (and passing the filename as the first parameter, argc/argv in C language for example)
Windows relies on some file extension to know if a file is executable, while Unix/Mac relies on a particular flag (x) associated with the file
Two things that are not well known about file extensions: directory names can have extension too, and extension can be way longer than the usual 3 characters.
With the help of file extension, you know how to read the first few and all the rest of the bytes. You also know what program to use to read the file. Or if it is an executable, you know that it is to be executed and not shown as a picture.
Yes you can change the file extension, but what does it mean then? It only means that OS (or any program that tried to read the file) is working correctly. Only you are providing bad data to it.
File extension is not something that some bytes of data inherently have. Extensions are given to those bytes depending upon the protocol followed to write them that way. After you have encoded the letters in binary form, you provide that binary form with .txt extension so that the text reader knows that these bytes convert to letters. That's the role of file extension. With bad file extension, this role is not fulfilled, resulting in incomprehension of the data you saved in binary.
As a general question: What's the role of file extension when determining file types?
The file extension usually identifies the application that opens a file.
If you rename a .JPG to a .PNG and while having JPG and PNG opened by the same application (usually an image viewer) that application can read the image stream and process it correctly regardless of having an incorrect file stream.
The problem arises if you rename the file in such a way that the file gets routed to an application that cannot handle the file's content.
If you rename a .DOCX (word) file to an Autocad extension (.DWG), opening the word file in autocad is likely to produce errors (unless per chance autocad can read word files).
just had a general question about how to approach a certain problem I'm facing. I'm fairly new to C so bear with me here. Say I have a folder with 1000+ text files, the files are not named in any kind of numbered order, but they are alphabetical. For my problem I have files of stock data, each file is named after the company's respective ticker. I want to write a program that will open each file, read the data find the historical low and compare it to the current price and calculate the percent change, and then print it. Searching and calculating are not a problem, the problem is getting the program to go through and open each file. The only way I can see to attack this is to create a text file containing all of the ticker symbols, having the program read that into an array and then run a loop that first opens the first filename in the array, perform the calculations, print the output, close the file, then loop back around moving to the second element (the next ticker symbol) in the array. This would be fairly simple to set up (I think) but I'd really like to avoid typing out over a thousand file names into a text file. Is there a better way to approach this? Not really asking for code ( unless there is some amazing function in c that will do this for me ;) ), just some advice from more experienced C programmers.
Thanks :)
Edit: This is on Linux, sorry I forgot to metion that!
Under Linux/Unix (BSD, OS X, POSIX, etc.) you can use opendir / readdir to go through the directory structure. No need to generate static files that need to be updated, when the file system has the information you want. If you only want a sub-set of stocks at a given time, then using glob would be quicker, there is also scandir.
I don't know what Win32 (Windows / Platform SDK) functions are called, if you are developing using Visual C++ as your C compiler. Searching MSDN Library should help you.
Assuming you're running on linux...
ls /path/to/text/files > names.txt
is exactly what you want.
opendir(); on linux.
http://linux.die.net/man/3/opendir
Exemple :
http://snippets.dzone.com/posts/show/5734
In pseudo code it would look like this, I cannot define the code as I'm not 100% sure if this is the correct approach...
for each directory entry
scan the filename
extract the ticker name from the filename
open the file
read the data
create a record consisting of the filename, data.....
close the file
add the record to a list/array...
> sort the list/array into alphabetical order based on
the ticker name in the filename...
You could vary it slightly if you wish, scan the filenames in the directory entries and sort them first by building a record with the filenames first, then go back to the start of the list/array and open each one individually reading the data and putting it into the record then....
Hope this helps,
best regards,
Tom.
There are no functions in standard C that have any notion of a "directory". You will need to use some kind of platform-specific function to do this. For some examples, take a look at this post from Cprogrammnig.com.
Personally, I prefer using the opendir()/readdir() approach as shown in the second example. It works natively under Linux and also on Windows if you are using Cygwin.
Approach 1) I would just have a specific directory in which I have ONLY these files containing the ticker data and nothing else. I would then use the C readdir API to list all files in the directory and iterate over each one performing the data processing that you require. Which ticker the file applies to is determined only by the filename.
Pros: Easy to code
Cons: It really depends where the files are stored and where they come from.
Approach 2) Change the file format so the ticker files start with a magic code identifying that this is a ticker file, and a string containing the name. As before use readdir to iterate through all files in the folder and open each file, ensure that the magic number is set and read the ticker name from the file, and process the data as before
Pros: More flexible than before. Filename needn't reflect name of ticker
Cons: Harder to code, file format may be fixed.
but I'd really like to avoid typing out over a thousand file names into a text file. Is there a better way to approach this?
I have solved the exact same problem a while back, albeit for personal uses :)
What I did was to use the OS shell commands to generate a list of those files and redirected the output to a text file and had my program run through them.
On UNIX, there's the handy glob function:
glob_t results;
memset(&results, 0, sizeof(results));
glob("*.txt", 0, NULL, &results);
for (i = 0; i < results.gl_pathc; i++)
printf("%s\n", results.gl_pathv[i]);
globfree(&results);
On Linux or a related system, you could use the fts library. It's designed for traversing file hierarchies: man fts,
or even something as simple as readdir
If on Windows, you can use their Directory Management API's. More specifically, the FindFirstFile function, used with wildcards, in conjunction with FindNextFile
I'm not asking about general syntactic rules for file names. I mean gotchas that jump out of nowhere and bite you. For example, trying to name a file "COM<n>" on Windows?
From: http://www.grouplogic.com/knowledge/index.cfm/fuseaction/view_Info/docID/111.
The following characters are invalid as file or folder names on Windows using NTFS: / ? < > \ : * | " and any character you can type with the Ctrl key.
In addition to the above illegal characters the caret ^ is also not permitted under Windows Operating Systems using the FAT file system.
Under Windows using the FAT file system file and folder names may be up to 255 characters long.
Under Windows using the NTFS file system file and folder names may be up to 256 characters long.
Under Window the length of a full path under both systems is 260 characters.
In addition to these characters, the following conventions are also illegal:
Placing a space at the end of the name
Placing a period at the end of the name
The following file names are also reserved under Windows:
aux,
com1,
com2,
...
com9,
lpt1,
lpt2,
...
lpt9,
con,
nul,
prn
Full description of legal and illegal filenames on Windows: http://msdn.microsoft.com/en-us/library/aa365247.aspx
A tricky Unix gotcha when you don't know:
Files which start with - or -- are legal but a pain in the butt to work with, as many command line tools think you are providing options to them.
Many of those tools have a special marker "--" to signal the end of the options:
gzip -9vf -- -mydashedfilename
As others have said, device names like COM1 are not possible as filenames under Windows because they are reserved devices.
However, there is an escape method to create and access files with these reserved names, for example, this command will redirect the output of the ver command into a file called COM1:
ver > "\\?\C:\Users\username\COM1"
Now you will have a file called COM1 that 99% of programs won't be able to open, and will probably freeze if you try to access.
Here's the Microsoft article that explains how this "file namespace" works. Basically it tells Windows not to do any string processing on the text and to pass it straight through to the filesystem. This trick can also be used to work with paths longer than 260 characters.
The boost::filesystem Portability Guide has a lot of good info.
Well, for MSDOS/Windows, NUL, PRN, LPT<n> and CON. They even cause problems if used with an extension: "NUL.TXT"
Unless you're touching special directories, the only illegal names on Linux are '.' and '..'. Any other name is possible, although accessing some of them from the shell requires using escape sequences.
EDIT: As Vinko Vrsalovic said, files starting with '-' and '--' are a pain from the shell, since those character sequences are interpreted by the application, not the shell.