file

Give a description of the type of the specified file. Works fine for files with no file extension

Look inside a zipped file and determine the file type(s) inside


Allow file to work with special or device files


Don't stop at first file type match; keep going until the end of the file


Determine the MIME encoding type of a file

file [ ][ file ][ file ] file ...

file [ ] file ...

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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

" 1." 4 If file does not exist, cannot be read, or its file status could not be determined, the output shall indicate that the file was processed, but that its type could not be determined.

" 2." 4 If the file is not a regular file, its file type shall be identified. The file types directory, FIFO, socket, block special, and character special shall be identified as such. Other implementation-defined file types may also be identified. If file is a symbolic link, by default the link shall be resolved and file shall test the type of file referenced by the symbolic link. (See the and options below.)

" 3." 4 If the length of file is zero, it shall be identified as an empty file.

" 4." 4 The file utility shall examine an initial segment of file and shall make a guess at identifying its contents based on position-sensitive tests. (The answer is not guaranteed to be correct; see the , , and options below.)

" 5." 4 The file utility shall examine file and make a guess at identifying its contents based on context-sensitive default system tests. (The answer is not guaranteed to be correct.)

" 6." 4 The file shall be identified as a data file.

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

If file is a symbolic link, by default the link shall be resolved and file shall test the type of file referenced by the symbolic link.

The file utility shall conform to the Base Definitions volume of POSIX.1 Section 12.2,Utility Syntax Guidelines, except that the order of the , , and options shall be significant.

The following options shall be supported by the implementation:

" "10 Apply any position-sensitive default system tests and context-sensitive default system tests to the file. This is the default if no or option is specified.

" "10 When a symbolic link is encountered, identify the file as a symbolic link. If is not specified and file is a symbolic link that refers to a nonexistent file, file shall identify the file as a symbolic link, as if had been specified.

" "10 If a file is a regular file, do not attempt to classify the type of the file further, but identify the file as specified in the STDOUT section.

" file "10 Specify the name of a file containing position-sensitive tests that shall be applied to a file in order to classify it (see the EXTENDED DESCRIPTION). No position-sensitive default system tests nor context-sensitive default system tests shall be applied unless the option is also specified.

" file "10 Specify the name of a file containing position-sensitive tests that shall be applied to a file in order to classify it (see the EXTENDED DESCRIPTION).

If the option is specified without specifying the option or the option, position-sensitive default system tests shall be applied after the position-sensitive tests specified by the option. If the option is specified with the option, the option, or both, or the option is specified with the option, the concatenation of the position-sensitive tests specified by these options shall be applied in the order specified by the appearance of these options. If a or file option-argument is , the results are unspecified.

The following operand shall be supported:

" file "10 A pathname of a file to be tested.

The standard input shall be used if a file operand is ' and the implementation treats the ' as meaning standard input. Otherwise, the standard input shall not be used.

The file can be any file type.

The following environment variables shall affect the execution of file:

" LANG "10 Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1 Section 8.2,Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)

" LC_ALL "10 If set to a non-empty string value, override the values of all the other internationalization variables.

" LC_CTYPE "10 Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files).

" LC_MESSAGES "10
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 "10 Determine the location of message catalogs for the processing of LC_MESSAGES.

Default.

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

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"%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 >shall contain (but is not limited to) the corresponding string, unless the file is identified by a position-sensitive test specified by a or option. Each <space> shown in the strings shall be exactly one <space>.

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1 Table4-9: File Utility Output Strings center tab(@) box; cB | cB | cB l | l | l. If file is:@< type >shall contain the string:@Notes _ Nonexistent@cannot open

Block special@block special@1 Character special@character special@1 Directory@directory@1 FIFO@fifo@1 Socket@socket@1 Symbolic link@symbolic link to@1 Regular file@regular file@1,2 Empty regular file@empty@3 Regular file that cannot be read@cannot open@3

Executable binary@executable@3,4,6 ar archive library (see ar )@archive@3,4,6 Extended cpio format (see pax )@cpioarchive@3,4,6 Extended tar format (see ustar in pax )@tararchive@3,4,6

Shell script@commands text@3,5,6 C-language source@c program text@3,5,6 FORTRAN source@fortran program text@3,5,6

Regular file whose type cannot be determined@data@3

10 Notes:

" 1." 4 This is a file type test.

" 2." 4 This test is applied only if the option is specified.

" 3." 4 This test is applied only if the option is not specified.

" 4." 4 This is a position-sensitive default system test.

" 5." 4 This is a context-sensitive default system test.

" 6." 4 Position-sensitive default system tests and context-sensitive default system tests are not applied if the option is specified unless the option is also specified.



In the POSIX locale, if file is identified as a symbolic link (see the option), the following alternative output format shall be used:

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



If the file named by the file operand does not exist, cannot be read, or the type of the file named by the file operand cannot be determined, this shall not be considered an error that affects the exit status.

The standard error shall be used only for diagnostic messages.

None.

A file specified as an option-argument to the or options shall contain one position-sensitive test per line, which shall be applied to the file. If the test succeeds, the message field of the line shall be printed and no further tests shall be applied, with the exception that tests on immediately following lines beginning with a single '>' character shall be applied.

Each line shall be composed of the following four <tab>-separated fields. (Implementations may allow any combination of one or more white-space characters other than <newline> to act as field separators.)

" offset "10 An unsigned number (optionally preceded by a single '>' character) specifying the offset, in bytes, of the value in the file that is to be compared against the value field of the line. If the file is shorter than the specified offset, the test shall fail.

If the offset begins with the character '>', the test contained in the line shall not be applied to the file unless the test on the last line for which the offset did not begin with a '>' was successful. By default, the offset shall be interpreted as an unsigned decimal number. With a leading 0x or 0X, the offset shall be interpreted as a hexadecimal number; otherwise, with a leading 0, the offset shall be interpreted as an octal number.

" type "10 The type of the value in the file to be tested. The type shall consist of the type specification characters d, s, and u, specifying signed decimal, string, and unsigned decimal, respectively.

The type string shall be interpreted as the bytes from the file starting at the specified offset and including the same number of bytes specified by the value field. If insufficient bytes remain in the file past the offset to match the value field, the test shall fail.

The type specification characters d and u can be followed by an optional unsigned decimal integer that specifies the number of bytes represented by the type. The type specification characters d and u can be followed by an optional C, S, I, or L, indicating that the value is of type char, short, int, or long, respectively.

The default number of bytes represented by the type specifiers d, f, and u shall correspond to their respective C-language types as follows. If the system claims conformance to the C-Language Development Utilities option, those specifiers shall correspond to the default sizes used in the c99 utility. Otherwise, the default sizes shall be implementation-defined.

For the type specifier characters d and u, the default number of bytes shall correspond to the size of a basic integer type of the implementation. For these specifier characters, the implementation shall support values of the optional number of bytes to be converted corresponding to the number of bytes in the C-language types char, short, int, or long. These numbers can also be specified by an application as the characters C, S, I, and L, respectively. The byte order used when interpreting numeric values is implementation-defined, but shall correspond to the order in which a constant of the corresponding type is stored in memory on the system.

All type specifiers, except for s, can be followed by a mask specifier of the form & number .The mask value shall be AND'ed with the value of the input file before the comparison with the value field of the line is made. By default, the mask shall be interpreted as an unsigned decimal number. With a leading 0x or 0X, the mask shall be interpreted as an unsigned hexadecimal number; otherwise, with a leading 0, the mask shall be interpreted as an unsigned octal number.

The strings byte, short, long, and string shall also be supported as type fields, being interpreted as dC, dS, dL, and s, respectively.

" value "10 The value to be compared with the value from the file.

If the specifier from the type field is s or string, then interpret the value as a string. Otherwise, interpret it as a number. If the value is a string, then the test shall succeed only when a string value exactly matches the bytes from the file.

If the value is a string, it can contain the following sequences:

" \ character "12 The <backslash>-escape sequences as specified in the Base Definitions volume of POSIX.1 Table 5-1,Escape Sequences and Associated Actions ( '\\', '\a', '\b', '\f', '\n', '\r', '\t', '\v'). In addition, the escape sequence '\' (the <backslash> character followed by a <space> character) shall be recognized to represent a <space> character. The results of using any other character, other than an octal digit, following the <backslash> are unspecified.

" \ octal "12 Octal sequences that can be used to represent characters with specific coded values. An octal sequence shall consist of a <backslash> followed by the longest sequence of one, two, or three octal-digit characters (01234567).

By default, any value that is not a string shall be interpreted as a signed decimal number. Any such value, with a leading 0x or 0X, shall be interpreted as an unsigned hexadecimal number; otherwise, with a leading zero, the value shall be interpreted as an unsigned octal number.

If the value is not a string, it can be preceded by a character indicating the comparison to be performed. Permissible characters and the comparisons they specify are as follows:

" = "6 The test shall succeed if the value from the file equals the value field.

" < "6 The test shall succeed if the value from the file is less than the value field.

" > "6 The test shall succeed if the value from the file is greater than the value field.

" & "6 The test shall succeed if all of the set bits in the value field are set in the value from the file.

" ^ "6 The test shall succeed if at least one of the set bits in the value field is not set in the value from the file.

" x "6 The test shall succeed if the file is large enough to contain a value of the type specified starting at the offset specified.

" message "10 The message to be printed if the test succeeds. The message shall be interpreted using the notation for the printf formatting specification; see printf. If the value field was a string, then the value from the file shall be the argument for the printf formatting specification; otherwise, the value from the file shall be the argument.

The following exit values shall be returned:

" 0" 6 Successful completion.

>0 6 An error occurred.

Default.

Thefollowingsectionsareinformative.

The file utility can only be required to guess at many of the file types because only exhaustive testing can determine some types with certainty. For example, binary data on some implementations 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. Note also that on systems that recognize shell script files starting with as executable files, these may be identified as executable binary files rather than as shell scripts.

Determine whether an argument is a binary executable file:

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file "$1" | grep ':.*executable' && printf "%s is executable. \ n$1"