can some body tell me what is the command to know the extension of the file?
for eg:
if i have a file called lol.txt , will it be command to know this file is a .txt file?

I am missing something here.....Can you not just do a listing (ls) and look at the file names?
Please give more information about what you are trying to do.

If what you want to know is what kind of data is stored in the file, then you probably want to use the "file" command.

To get the file extension of all files in a directory, you might do something like:

linux doesn't really use file extensions like windows does.. It's more of a place holder. the file lol and lol.txt are essentially the same file and linux doesn't really know the difference. You can do a vi on them both and get the same results. It just makes things easier for people coming over from windows to see a file with a .txt to know that is a text file.. OR if you are transferring data from a linux PC to a windows PC and you want to be able to read that file in notepad you'll need the .txt extension so you can open it automatically by clicking on it rather than, right click, open with, notepad.

maybe i'm over thinking what you are asking.. If you just want to see that lol.txt has a txt extension you just do
ls
or
ls -l

If you want to identify a file based on the contents, rather than the extension, then you want to use the "file" command, as someone stated above.

In the Unix world, it treats all files as either ASCII or Binary, it's really either or if given in a nutshell. I won't go into devices or the such but yeah, extensions are really just to let you know what type of file it is.

I back up pixellany 'ls' shows all files by their name. If their name is lol.txt or lol.txt.txt.txt or lol-txt-txt it does not matter its just the file name. The txt in the name just helps us know its an ASCII instead of a binary file.

I never thought about that but your right. Humm learn something everyday. ;-)

I think the problem is that he is coming from a DOS evnt. Where it matters what extension the file uses and Windows sometimes hides them.

The short answer is that
In Linux you do not need extensions. They are nice but not needed for most things

it looked like he was asking how to verify the type of the file regardless of the extension..
His example even states he has a file called lol.txt and wanted to know how to verify it is indeed a text file

in which case the file command would be the proper one to use, as stated earlier.

Actually he's explicitly asking how to verify that a .txt file
is a .txt file (not "a file containing text"), and asks in the
title to know the extension type, which brings us back to
visual examination and ls ;}



Cheers,
Tink

The command stat will also do. Along with ls like mentioned. I think it's good though that myself and other members explained how files are treated in *nix, just an added detail to benefit the OP.