file (1) Linux Manual Page

NAME

file – determine file type

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 ]

DESCRIPTION

This manual page documents version 5.41 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 In 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 In elf.h , In a.out.h and possibly In 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 /etc/magic and the compiled magic file /usr/share/misc/magic.mgc or the files in the directory /usr/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. In 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”

OPTIONS

–apple

Causes the file command to output the file type and creator code as used by older MacOS versions. The code consists of eight letters, the first describing the file type, the latter the creator. This option works properly only for file formats that have the apple-style output defined.

-b , –brief

Do not prepend filenames to output lines (brief mode).

-C , –compile

Write a magic.mgc output file that contains a pre-parsed version of the magic file or directory.

-c , –checking-printout

Cause a checking printout of the parsed form of the magic file. This is usually used in conjunction with the –m option to debug a new magic file before installing it.

-d

Prints internal debugging information to stderr.

-E

On filesystem errors (file not found etc), instead of handling the error as regular output as POSIX mandates and keep going, issue an error message and exit.

-e , –exclude testname

Exclude the test named in testname from the list of tests made to determine the file type. Valid test names are:

apptype

EMX application type (only on EMX).

ascii

Various types of text files (this test will try to guess the text encoding, irrespective of the setting of the `encoding’ option).

encoding

Different text encodings for soft magic tests.

tokens

Ignored for backwards compatibility.

cdf

Prints details of Compound Document Files.

compress

Checks for, and looks inside, compressed files.

csv

Checks Comma Separated Value files.

elf

Prints ELF file details, provided soft magic tests are enabled and the elf magic is found.

json

Examines JSON (RFC-7159) files by parsing them for compliance.

soft

Consults magic files.

tar

Examines tar files by verifying the checksum of the 512 byte tar header. Excluding this test can provide more detailed content description by using the soft magic method.

text

A synonym for `ascii’

–exclude-quiet

Like –-exclude but ignore tests that file does not know about. This is intended for compatibility with older versions of file.

–extension

Print a slash-separated list of valid extensions for the file type found.

-F , –separator separator

Use the specified string as the separator between the filename and the file result returned. Defaults to `:’

-f , –files-from namefile

Read the names of the files to be examined from namefile (one per line) before the argument list. Either namefile or at least one filename argument must be present; to test the standard input, use `-‘ as a filename argument. Please note that namefile is unwrapped and the enclosed filenames are processed when this option is encountered and before any further options processing is done. This allows one to process multiple lists of files with different command line arguments on the same file invocation. Thus if you want to set the delimiter, you need to do it before you specify the list of files, like: “-F @ –f namefile ” instead of: “-f namefile –F file … ”

-h , –no-dereference

This option causes symlinks not to be followed (on systems that support symbolic links). This is the default if the environment variable POSIXLY_CORRECT is not defined.

-i , –mime

Causes the file command to output mime type strings rather than the more traditional human readable ones. Thus it may say `text/plain; charset=us-ascii’ rather than “ASCII text”

–mime-type , –mime-encoding

Like –i but print only the specified element(s).

-k , –keep-going

Don’t stop at the first match, keep going. Subsequent matches will be have the string `
– ‘ prepended. (If you want a newline, see the –r option.) The magic pattern with the highest strength (see the –l option) comes first.

-l , –list

Shows a list of patterns and their strength sorted descending by magic(5) strength which is used for the matching (see also the –k option).

-L , –dereference

This option causes symlinks to be followed, as the like-named option in ls(1) (on systems that support symbolic links). This is the default if the environment variable POSIXLY_CORRECT is defined.

-m , –magic-file magicfiles

Specify an alternate list of files and directories containing magic. This can be a single item, or a colon-separated list. If a compiled magic file is found alongside a file or directory, it will be used instead.

-N , –no-pad

Don’t pad filenames so that they align in the output.

-n , –no-buffer

Force stdout to be flushed after checking each file. This is only useful if checking a list of files. It is intended to be used by programs that want filetype output from a pipe.

-p , –preserve-date

On systems that support utime(3) or utimes(2), attempt to preserve the access time of files analyzed, to pretend that file never read them.

-P , –parameter name=value

Set various parameter limits.

Name Ta Default Ta Explanation

bytes Ta 1048576 Ta max number of bytes to read from file

elf_notes Ta 256 Ta max ELF notes processed

elf_phnum Ta 2048 Ta max ELF program sections processed

elf_shnum Ta 32768 Ta max ELF sections processed

encoding Ta 65536 Ta max number of bytes to scan for encoding evaluation

indir Ta 50 Ta recursion limit for indirect magic

name Ta 50 Ta use count limit for name/use magic

regex Ta 8192 Ta length limit for regex searches

-r , –raw

Don’t translate unprintable characters to \ooo. Normally file translates unprintable characters to their octal representation.

-s , –special-files

Normally, file only attempts to read and determine the type of argument files which stat(2) reports are ordinary files. This prevents problems, because reading special files may have peculiar consequences. Specifying the –s option causes file to also read argument files which are block or character special files. This is useful for determining the filesystem types of the data in raw disk partitions, which are block special files. This option also causes file to disregard the file size as reported by stat(2) since on some systems it reports a zero size for raw disk partitions.

-S , –no-sandbox

On systems where libseccomp ( https://github.com/seccomp/libseccomp is available, the –S option disables sandboxing which is enabled by default. This option is needed for file to execute external decompressing programs, i.e. when the –z option is specified and the built-in decompressors are not available. On systems where sandboxing is not available, this option has no effect.

Note: This Debian version of file was built without seccomp support, so this option has no effect.

-v , –version

Print the version of the program and exit.

-z , –uncompress

Try to look inside compressed files.

-Z , –uncompress-noreport

Try to look inside compressed files, but report information about the contents only not the compression.

-0 , –print0

Output a null character `