NAME

file - determine file type

 SYNOPSIS

file file ...

 DESCRIPTION

The file utility performs a series of tests on each specified file in an attempt to classify it:

1. If the file is not a regular file, its file type is identified. The file types directory, FIFO, block special and character special are identified as such. Other implementation-dependent file types may also be identified.

2. If the file is a regular file, and:

   1. The file is zero-length, it is identified as an empty file.

   2. The file is not zero-length, file will examine an initial segment of the file and make a guess at identifying its contents or whether it is an executable binary file. (The answer is not guaranteed to be correct.)

If file does not exist, cannot be read, or its file status could not be determined, the output will indicate that the file was processed, but that its type could not be determined.

 OPTIONS

None.

 OPERANDS

The following operand is supported:

file

A pathname of a file to be tested.

 STDIN

Not used.

 INPUT FILES

The file can be any file type.

 ENVIRONMENT VARIABLES

The following environment variables affect the execution of file:

LANG

Provide a default value for the internationalisation variables that are unset or null. If LANG is unset or null, the corresponding value from the implementation-dependent default locale will be used. If any of the internationalisation variables contains an invalid setting, the utility will behave as if none of the variables had been defined.

LC_ALL

If set to a non-empty string value, override the values of all the other internationalisation variables.

LC_CTYPE

Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single- as opposed to multi-byte characters in arguments and input files).

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error and informative messages written to standard output.

NLSPATH

Determine the location of message catalogues for the processing of LC_MESSAGES .

 ASYNCHRONOUS EVENTS

Default.

 STDOUT

In the POSIX locale, the following format is used to identify each operand, file specified:

"%s: %s\n", <file>, <type>

The values for <type> are unspecified, except that in the POSIX locale, if file is identified as one of the types listed in the following table, <type> will contain (but is not limited to) the corresponding string. Each space shown in the strings is exactly one space character.

If file is a:
<type> Contains the String:
directory
directory
FIFO
fifo
block special
block special
character special
character special
executable binary
executable
empty regular file
empty
ar archive library (see ar)
archive
extended cpio format (see pax)
cpio archive
extended tar format (see ustar - see pax)
tar archive
shell script
commands text
C-language source
c program text
FORTRAN source
fortran program text

 Table: File Utility Output Strings

If the file named by the file operand does not exist, cannot be read or the status of the file cannot be determined, the string cannot open will be included as part of the <type> field, but this is not considered an error that affects the exit status.

 STDERR

Used only for diagnostic messages.

 OUTPUT FILES

None.

 EXTENDED DESCRIPTION

None.

 EXIT STATUS

The following exit values are returned:

0

Successful completion.

>0

An error occurred.

 CONSEQUENCES OF ERRORS

Default.

 APPLICATION USAGE

The file utility can only be required to guess at many of the file types because only exhaustive testing can determine some types with certitude. For example, binary data on some systems might match the initial segment of an executable or a tar archive.

Note that the table indicates that the output contains the stated string. Systems may add text before or after the string. For executables, as an example, the machine architecture and various facts about how the file was link-edited may be included.

 EXAMPLES

Determine if an argument is a binary executable file:

file "$1" | grep -Fq executable &&
    printf "%s is executable.\n" "$1"

 FUTURE DIRECTIONS

None.

 SEE ALSO

ls.