определить тип файла (determine file type)
Имя (Name)
file — determine file type
Синопсис (Synopsis)
file [-bcdEhiklLNnprsSvzZ0] [--apple] [--exclude-quiet]
[--extension] [--mime-encoding] [--mime-type] [-e testname]
[-F separator] [-f namefile] [-m magicfiles] [-P name=value]
file ...
file -C [-m magicfiles]
file [--help]
Описание (Description)
This manual page documents version 5.40 of the file command.
file tests each argument in an attempt to classify it. There are
three sets of tests, performed in this order: filesystem tests,
magic tests, and language tests. The first test that succeeds
causes the file type to be printed.
The type printed will usually contain one of the words text (the
file contains only printing characters and a few common control
characters and is probably safe to read on an ASCII terminal),
executable (the file contains the result of compiling a program in
a form understandable to some UNIX kernel or another), or data
meaning anything else (data is usually 'binary' or non-printable).
Exceptions are well-known file formats (core files, tar archives)
that are known to contain binary data. When modifying magic files
or the program itself, make sure to preserve these keywords. Users
depend on knowing that all the readable files in a directory have
the word 'text' printed. Don't do as Berkeley did and change
'shell commands text' to 'shell script'.
The filesystem tests are based on examining the return from a
stat(2) system call. The program checks to see if the file is
empty, or if it's some sort of special file. Any known file types
appropriate to the system you are running on (sockets, symbolic
links, or named pipes (FIFOs) on those systems that implement them)
are intuited if they are defined in the system header file
<sys/stat.h>.
The magic tests are used to check for files with data in particular
fixed formats. The canonical example of this is a binary
executable (compiled program) a.out file, whose format is defined
in <elf.h>, <a.out.h> and possibly <exec.h> in the standard include
directory. These files have a 'magic number' stored in a
particular place near the beginning of the file that tells the UNIX
operating system that the file is a binary executable, and which of
several types thereof. The concept of a 'magic number' has been
applied by extension to data files. Any file with some invariant
identifier at a small fixed offset into the file can usually be
described in this way. The information identifying these files is
read from the compiled magic file /usr/local/share/misc/magic.mgc,
or the files in the directory /usr/local/share/misc/magic if the
compiled file does not exist. In addition, if $HOME/.magic.mgc or
$HOME/.magic exists, it will be used in preference to the system
magic files.
If a file does not match any of the entries in the magic file, it
is examined to see if it seems to be a text file. ASCII,
ISO-8859-x, non-ISO 8-bit extended-ASCII character sets (such as
those used on Macintosh and IBM PC systems), UTF-8-encoded Unicode,
UTF-16-encoded Unicode, and EBCDIC character sets can be
distinguished by the different ranges and sequences of bytes that
constitute printable text in each set. If a file passes any of
these tests, its character set is reported. ASCII, ISO-8859-x,
UTF-8, and extended-ASCII files are identified as 'text' because
they will be mostly readable on nearly any terminal; UTF-16 and
EBCDIC are only 'character data' because, while they contain text,
it is text that will require translation before it can be read. In
addition, file will attempt to determine other characteristics of
text-type files. If the lines of a file are terminated by CR,
CRLF, or NEL, instead of the Unix-standard LF, this will be
reported. Files that contain embedded escape sequences or
overstriking will also be identified.
Once file has determined the character set used in a text-type
file, it will attempt to determine in what language the file is
written. The language tests look for particular strings (cf.
<names.h>) that can appear anywhere in the first few blocks of a
file. For example, the keyword .br indicates that the file is most
likely a troff(1) input file, just as the keyword struct indicates
a C program. These tests are less reliable than the previous two
groups, so they are performed last. The language test routines
also test for some miscellany (such as tar(1) archives, JSON
files).
Any file that cannot be identified as having been written in any of
the character sets listed above is simply said to be 'data'.
