How can I show all file types contained in a directory?

Is there any command which tells me in the specific directory which types of files exist?

I can find out the file type by using a command like od -c myfile | less.

But I don't know how to do it for all files in a directory.

Although od -c will indeed show the contents of a file, it is not a good way to get its file type. While some files will contain a header with the file type, not all will. A better way is the command file:

$ echo "hello" > foo.txt
$ file foo.txt
foo.txt: ASCII text

So, to get a list of all file types in a directory, you can do:

for file in dir/*; do file "$file" | cut -d: -f 2; done | sort -u

Example output:

 PNG image data, 1500 x 500, 8-bit/color RGBA, non-interlaced
 ASCII text
 directory
 GIF image data, version 89a, 22 x 22
 ELF 64-bit LSB  executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=becf821e4d814fdb69306d0b3f686eb06992f5e5, stripped

Explanation

• for file in dir/*; do ... done; : iterate through everything in dir (dir is just an example, you should change this to the name of the actual directory you want to search through), saving each item in turn as $file
• file "$file" : run file on each of the items found.
• cut -d: -f 2 : print only the second field (fields defined by :)
• sed 's/^ //; s/ +/ /g' : remove spaces from the beginning of the line and convert consecutive spaces into a single space.
• sort -u : remove duplicate file types

I would probably do something like this -

find . -type f -exec file {}  \;

That will search from the current path, for files (e.g. no directories) and then execute the file command on each file.