libmagic(3) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | FILES | SEE ALSO | BUGS | AUTHORS | COLOPHON

LIBMAGIC(3)           BSD Library Functions Manual           LIBMAGIC(3)

NAME         top

     magic_open, magic_close, magic_error, magic_errno,
     magic_descriptor, magic_buffer, magic_getflags, magic_setflags,
     magic_check, magic_compile, magic_list, magic_load,
     magic_load_buffers, magic_setparam, magic_getparam, magic_version —
     Magic number recognition library

LIBRARY         top

     Magic Number Recognition Library (libmagic, -lmagic)

SYNOPSIS         top

     #include <magic.h>

     magic_t
     magic_open(int flags);

     void
     magic_close(magic_t cookie);

     const char *
     magic_error(magic_t cookie);

     int
     magic_errno(magic_t cookie);

     const char *
     magic_descriptor(magic_t cookie, int fd);

     const char *
     magic_file(magic_t cookie, const char *filename);

     const char *
     magic_buffer(magic_t cookie, const void *buffer, size_t length);

     int
     magic_getflags(magic_t cookie);

     int
     magic_setflags(magic_t cookie, int flags);

     int
     magic_check(magic_t cookie, const char *filename);

     int
     magic_compile(magic_t cookie, const char *filename);

     int
     magic_list(magic_t cookie, const char *filename);

     int
     magic_load(magic_t cookie, const char *filename);

     int
     magic_load_buffers(magic_t cookie, void **buffers, size_t *sizes,
         size_t nbuffers);

     int
     magic_getparam(magic_t cookie, int param, void *value);

     int
     magic_setparam(magic_t cookie, int param, const void *value);

     int
     magic_version(void);

DESCRIPTION         top

     These functions operate on the magic database file which is
     described in magic(4).

     The function magic_open() creates a magic cookie pointer and
     returns it.  It returns NULL if there was an error allocating the
     magic cookie.  The flags argument specifies how the other magic
     functions should behave:

     MAGIC_NONE      No special handling.

     MAGIC_DEBUG     Print debugging messages to stderr.

     MAGIC_SYMLINK   If the file queried is a symlink, follow it.

     MAGIC_COMPRESS  If the file is compressed, unpack it and look at
                     the contents.

     MAGIC_DEVICES   If the file is a block or character special device,
                     then open the device and try to look in its
                     contents.

     MAGIC_MIME_TYPE
                     Return a MIME type string, instead of a textual
                     description.

     MAGIC_MIME_ENCODING
                     Return a MIME encoding, instead of a textual
                     description.

     MAGIC_MIME      A shorthand for MAGIC_MIME_TYPE |
                     MAGIC_MIME_ENCODING.

     MAGIC_CONTINUE  Return all matches, not just the first.

     MAGIC_CHECK     Check the magic database for consistency and print
                     warnings to stderr.

     MAGIC_PRESERVE_ATIME
                     On systems that support utime(3) or utimes(2),
                     attempt to preserve the access time of files
                     analysed.

     MAGIC_RAW       Don't translate unprintable characters to a \ooo
                     octal representation.

     MAGIC_ERROR     Treat operating system errors while trying to open
                     files and follow symlinks as real errors, instead
                     of printing them in the magic buffer.

     MAGIC_APPLE     Return the Apple creator and type.

     MAGIC_EXTENSION
                     Return a slash-separated list of extensions for
                     this file type.

     MAGIC_COMPRESS_TRANSP
                     Don't report on compression, only report about the
                     uncompressed data.

     MAGIC_NO_CHECK_APPTYPE
                     Don't check for EMX application type (only on EMX).

     MAGIC_NO_CHECK_CDF
                     Don't get extra information on MS Composite
                     Document Files.

     MAGIC_NO_CHECK_COMPRESS
                     Don't look inside compressed files.

     MAGIC_NO_CHECK_ELF
                     Don't print ELF details.

     MAGIC_NO_CHECK_ENCODING
                     Don't check text encodings.

     MAGIC_NO_CHECK_SOFT
                     Don't consult magic files.

     MAGIC_NO_CHECK_TAR
                     Don't examine tar files.

     MAGIC_NO_CHECK_TEXT
                     Don't check for various types of text files.

     MAGIC_NO_CHECK_TOKENS
                     Don't look for known tokens inside ascii files.

     MAGIC_NO_CHECK_JSON
                     Don't examine JSON files.

     MAGIC_NO_CHECK_CSV
                     Don't examine CSV files.

     The magic_close() function closes the magic(4) database and
     deallocates any resources used.

     The magic_error() function returns a textual explanation of the
     last error, or NULL if there was no error.

     The magic_errno() function returns the last operating system error
     number (errno(2)) that was encountered by a system call.

     The magic_file() function returns a textual description of the
     contents of the filename argument, or NULL if an error occurred.
     If the filename is NULL, then stdin is used.

     The magic_descriptor() function returns a textual description of
     the contents of the fd argument, or NULL if an error occurred.

     The magic_buffer() function returns a textual description of the
     contents of the buffer argument with length bytes size.

     The magic_getflags() functions returns a value representing current
     flags set.

     The magic_setflags() function sets the flags described above.  Note
     that using both MIME flags together can also return extra
     information on the charset.

     The magic_check() function can be used to check the validity of
     entries in the colon separated database files passed in as
     filename, or NULL for the default database.  It returns 0 on
     success and -1 on failure.

     The magic_compile() function can be used to compile the colon
     separated list of database files passed in as filename, or NULL for
     the default database.  It returns 0 on success and -1 on failure.
     The compiled files created are named from the basename(1) of each
     file argument with “.mgc” appended to it.

     The magic_list() function dumps all magic entries in a human
     readable format, dumping first the entries that are matched against
     binary files and then the ones that match text files.  It takes and
     optional filename argument which is a colon separated list of
     database files, or NULL for the default database.

     The magic_load() function must be used to load the colon separated
     list of database files passed in as filename, or NULL for the
     default database file before any magic queries can performed.

     The default database file is named by the MAGIC environment
     variable.  If that variable is not set, the default database file
     name is /usr/local/share/misc/magic.  magic_load() adds “.mgc” to
     the database filename as appropriate.

     The magic_load_buffers() function takes an array of size nbuffers
     of buffers with a respective size for each in the array of sizes
     loaded with the contents of the magic databases from the
     filesystem.  This function can be used in environment where the
     magic library does not have direct access to the filesystem, but
     can access the magic database via shared memory or other IPC means.

     The magic_getparam() and magic_setparam() allow getting and setting
     various limits related to the magic library.

           Parameter                    Type      Default
           MAGIC_PARAM_INDIR_MAX        size_t    15
           MAGIC_PARAM_NAME_MAX         size_t    30
           MAGIC_PARAM_ELF_NOTES_MAX    size_t    256
           MAGIC_PARAM_ELF_PHNUM_MAX    size_t    128
           MAGIC_PARAM_ELF_SHNUM_MAX    size_t    32768
           MAGIC_PARAM_REGEX_MAX        size_t    8192
           MAGIC_PARAM_BYTES_MAX        size_t    1048576

     The MAGIC_PARAM_INDIR_RECURSION parameter controls how many levels
     of recursion will be followed for indirect magic entries.

     The MAGIC_PARAM_NAME_RECURSION parameter controls how many levels
     of recursion will be followed for for name/use calls.

     The MAGIC_PARAM_NAME_MAX parameter controls the maximum number of
     calls for name/use.

     The MAGIC_PARAM_NOTES_MAX parameter controls how many ELF notes
     will be processed.

     The MAGIC_PARAM_PHNUM_MAX parameter controls how many ELF program
     sections will be processed.

     The MAGIC_PARAM_SHNUM_MAX parameter controls how many ELF sections
     will be processed.

     The magic_version() command returns the version number of this
     library which is compiled into the shared library using the
     constant MAGIC_VERSION from <magic.h>.  This can be used by client
     programs to verify that the version they compile against is the
     same as the version that they run against.

RETURN VALUES         top

     The function magic_open() returns a magic cookie on success and
     NULL on failure setting errno to an appropriate value.  It will set
     errno to EINVAL if an unsupported value for flags was given.  The
     magic_list(), magic_load(), magic_compile(), and magic_check()
     functions return 0 on success and -1 on failure.  The
     magic_buffer(), magic_getpath(), and magic_file(), functions return
     a string on success and NULL on failure.  The magic_error()
     function returns a textual description of the errors of the above
     functions, or NULL if there was no error.  The magic_version()
     always returns the version number of the library.  Finally,
     magic_setflags() returns -1 on systems that don't support utime(3),
     or utimes(2) when MAGIC_PRESERVE_ATIME is set.

FILES         top

     /usr/local/share/misc/magic      The non-compiled default magic
                                      database.
     /usr/local/share/misc/magic.mgc  The compiled default magic
                                      database.

SEE ALSO         top

     file(1), magic(4)

BUGS         top

     The results from magic_buffer() and magic_file() where the buffer
     and the file contain the same data can produce different results,
     because in the magic_file() case, the program can lseek(2) and
     stat(2) the file descriptor.

AUTHORS         top

     Måns Rullgård Initial libmagic implementation, and configuration.
     Christos Zoulas API cleanup, error code and allocation handling.

COLOPHON         top

     This page is part of the file (a file type guesser) project.
     Information about the project can be found at
     http://www.darwinsys.com/file/.  If you have a bug report for this
     manual page, see ⟨http://bugs.gw.com/my_view_page.php⟩.  This page
     was obtained from the project's upstream Git read-only mirror of
     the CVS repository ⟨https://github.com/glensc/file⟩ on 2021-04-01.
     (At that time, the date of the most recent commit that was found in
     the repository was 2021-04-01.)  If you discover any rendering
     problems in this HTML version of the page, or you believe there is
     a better or more up-to-date source for the page, or you have
     corrections or improvements to the information in this COLOPHON
     (which is not part of the original manual page), send a mail to
     man-pages@man7.org

BSD                           June 8, 2019                           BSD