On Unix-like operating systems, the file command reports a file’s type.

This page covers the Linux version of file.

Description

The file command 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.

  • Description
  • Syntax
  • Examples
  • Related commands
  • Linux commands help

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 a kernel), or data meaning anything else (usually binary or non-printable). Exceptions are well-known file formats (core files, tar archives) that are known to contain binary data.

The filesystem tests are based on examining the return from a stat 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 (first in first out) 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 operating system that the file is a binary executable, and which of several types thereof. The concept of a “magic” is 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. Also, 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 are mostly readable on nearly any terminal; UTF-16 and EBCDIC are only “character data” because, while they contain text, it is text that requires translation before it can be read. Also, the file attempts to determine other characteristics of text-type files. If the lines of a file are terminated by CR, CR LF, or NEL, instead of the Unix-standard LF, this will be reported. Files that contain embedded escape sequences or overstriking is also identified.

Once file has determined the character set used in a text-type file, it attempts 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 input file, 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 archives).

Any file that cannot be identified as having been written in any of the character sets listed above is said to be “data.”

Syntax

file [-bchiklLNnprsvz0] [–apple] [–mime-encoding] [–mime-type] [-e testname] [-F separator] [-f namefile] [-m magicfiles] file …

file -C [-m magicfiles]

file [–help]

Options

Examples

file *

Below is an example of what may appear when running file with a wildcard for all files:

shutdown.htm: HTML document text si.htm: HTML document text side0.gif: GIF image data, version 89a, 107 x 18 robots.txt: ASCII text, with CRLF line terminators routehlp.htm: HTML document text rss: setgid directory

file *.txt

Below is an example of what may appear when running the above example; running the file command listing any file ending with .txt:

form.txt: news or mail text friend.txt: news or mail text ihave.txt: news or mail text index.txt: ASCII Java program text, with very long lines, with CRLF line terminators jargon.txt: news or mail text news.txt: Non-ISO extended-ASCII C program text, with very long lines, with CRLF line terminators newsdata.txt: Non-ISO extended-ASCII English text, with very long lines, with CRLF line terminators qad.txt: news or mail text refrence.txt: news or mail text robots.txt: ASCII text, with CRLF line terminators stopwords.txt: ASCII English text, with CRLF line terminators yhelp.txt: news or mail text

ls — List the contents of a directory or directories.