file - determine file type
/usr/bin/file [-dh] [-m mfile] [-M Mfile] [ -f ffile] file...
/usr/bin/file [-dh] [-m mfile] [-M Mfile] -f ffile
/usr/bin/file -i [-h] [ -f ffile] file...
/usr/bin/file -i [-h] -f ffile
/usr/bin/file -c [-d] [ -m mfile] [-M Mfile]
/usr/xpg4/bin/file [-dh] [ -m mfile] [-M Mfile] [-f ffile] file...
/usr/xpg4/bin/file [-dh] [ -m mfile] [-M Mfile] -f ffile
/usr/xpg4/bin/file -i [-h ] [-f ffile] file...
/usr/xpg4/bin/file -i [-h ] -f ffile
/usr/xpg4/bin/file -c [-d ] [-m mfile] [-M Mfile]
The file utility performs a series of tests on each file supplied by file and, optionally, on each file listed in ffile in an attempt to classify it. 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. If the file is a regular file and the file is zero-length, it is identified as an empty file.
If file appears to be a text file, file examines the first 512 bytes and tries to determine its programming language. If file is a symbolic link, by default the link is followed and file tests the file to which the symbolic link refers.
If file is a relocatable object, executable, or shared object, file prints out information about the file's execution requirements. This information includes the machine class, byte-ordering, static/dynamic linkage, and any software or hardware capability requirements. If file is a runtime linking configuration file, file prints information about the target platform, including the machine class and byte-ordering.
By default, file will try to use the localized magic file /usr/lib/locale/locale/LC_MESSAGES/magic, if it exists, to identify files that have a magic number. For example, in the Japanese locale, file will try to use /usr/lib/locale/ja/LC_MESSAGES/magic. If a localized magic file does not exist, file will utilize /etc/magic. A magic number is a numeric or string constant that indicates the file type. See magic(5) for an explanation of the format of /etc/magic.
If file does not exist, cannot be read, or its file status could not be determined, it is not considered an error that affects the exit status. The output will indicate that the file was processed, but that its type could not be determined.
The following options are supported:
Checks the magic file for format errors. For reasons of efficiency, this validation is normally not carried out.
Applies any position-sensitive and context-sensitive default system tests to the file.
ffile contains a list of the files to be examined.
When a symbolic link is encountered, this option identifies the file as a symbolic link. If –h is not specified and file is a symbolic link that refers to a non-existent file, the file utility identifies the file as a symbolic link, as if –h had been specified.
If a file is a regular file, this option does not attempt to classify the type of file further, but identifies the file as a “regular file”.
Uses mfile as an alternate magic file, instead of /etc/magic.
Specifies the name of a file containing position-sensitive tests that are applied to a file in order to classify it (see magic(5)). If the –m option is specified without specifying the –d option or the –M option, position-sensitive default system tests are applied after the position-sensitive tests specified by the –m option.
Specifies the name of a file containing position-sensitive tests that are applied to a file in order to classify it (see magic(5)). No position-sensitive default system tests nor context-sensitive default system tests are applied unless the –d option is also specified.
If the –M option is specified with the –d option, the –m option, or both, or if the –m option is specified with the –d option, the concatenation of the position-sensitive tests specified by these options is applied in the order specified by the appearance of these options. If a –M or –m file option-argument is -, then the results are unspecified.
The following operands are supported:
A path name 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 following example determine if an argument is a binary executable file:
file "$1" | grep −Fq executable && printf "%s is executable.\n" "$1"
See environ(7) for descriptions of the following environment variables that affect the execution of file: LANG, LC_ALL, LC_CTYPE , LC_MESSAGES, and NLSPATH.
The following exit values are returned:
An error occurred.
file's magic number file
See attributes(7) for descriptions of the following attributes:
The file utility cannot examine archive members unless they are first extracted from the archive into a separate file. The elffile utility can examine archive members in place, and is recommended for use with ELF objects and archives.