libmagic(3) — Linux manual page

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

LIBMAGIC(3)              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

       <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) const char *
       magic_getpath(const char *magicfile, int action)

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_COMPRESS_FORK
                       Don't allow decompressors that use fork.

       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.

       MAGIC_NO_CHECK_SIMH
                       Don't examine SIMH tape 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.

       The magic_getpath() command returns the colon separated list of
       magic database locations.  If the filename is non-NULL, then it
       is returned.  Otherwise, if the MAGIC environment variable is
       defined, then it is returned.  Otherwise, if action is 0 (meaning
       "file load"), then any user-specific magic database file is
       included.  Otherwise, only the system default magic database path
       is included.

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:https://www.darwinsys.com/file/.  If you have a bug report for
       this manual page, see ⟨http:https://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
       2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-21.)  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 [email protected]

GNU                           June 16, 2023                  LIBMAGIC(3)