file Command Practical Examples in Linux

Usage:
file [-c] [-h] [-m mfile] [-f ffile] names

* If the file cannot be read, its status undetermined, or its type undetermined, file will indicate that the file was processed and its type was undetermined.
* File must be able to determine the types directory, FIFO, socket, block special file, and character special file
* The file is identified as a data file
* Zero-length files are identified as such
* In most implementations, the file command uses a database to drive the probing of the lead bytes. That database is implemented in a file called magic, whose location is usually in /etc/magic, /usr/share/file/magic or a similar location.

Here’s the listing of example usage of “file” command:

1. To determine file type(file file_name/directory_name):

sanfoundry-> file india_map.cpp 
india_map.cpp: ASCII text
sanfoundry-> file tex.c
tex.c: C program text

2. To show whether file empty or not:

sanfoundry-> touch file.txt 
sanfoundry-> file file.txt 
file.txt: empty

3. To find drives in /dev and there types:

sanfoundry-> file /dev/hidraw0 
/dev/hidraw0: character special

4. To specify a file specially formatted containing position-sensitive tests(file -m File_name):

sanfoundry-> cat > 2.c 
Hi i am x.
I am a nice boy.
sanfoundry-> file -m 2.c 
2.c, 1: Warning: offset `Hi i am x.' invalid
2.c, 1: Warning: type `Hi i am x.' invalid
2.c, 2: Warning: offset `I am a nice boy.' invalid
2.c, 2: Warning: type `I am a nice boy.' invalid
file: could not find any magic files!

5. To perform default position-sensitive and context-sensitive tests to the given file(file -d file_name):

sanfoundry-> file -d 2.c 
........
 
> 0 search/1,!p,""]
18446744073709551576 != 0 = 1
mget @0: Hi i am x.\nI am a nice boy.\n\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000
 
>> 0 regex,=^package[ \t]+req,"Tcl script"]
1 == 0 = 0
ascmagic 1
2.c: ASCII text

NOTE
Some more useful options:
* -h, do-not-dereference symbolic links that point to an existing file or directory.
* -L, dereference the symbolic link that points to an existing file or directory.

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