magic_open(3) — Linux manual page


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 recogni‐
     tion library

LIBRARY         top

     Magic Number Recognition Library (libmagic, -lmagic)

SYNOPSIS         top

     #include <magic.h>

     magic_open(int flags);

     magic_close(magic_t cookie);

     const char *
     magic_error(magic_t cookie);

     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);

     magic_getflags(magic_t cookie);

     magic_setflags(magic_t cookie, int flags);

     magic_check(magic_t cookie, const char *filename);

     magic_compile(magic_t cookie, const char *filename);

     magic_list(magic_t cookie, const char *filename);

     magic_load(magic_t cookie, const char *filename);

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

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

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


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

     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

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

                     Return a MIME type string, instead of a textual

                     Return a MIME encoding, instead of a textual descrip‐


     MAGIC_CONTINUE  Return all matches, not just the first.

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

                     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

     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.

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

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

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

                     Don't get extra information on MS Composite Document

                     Don't look inside compressed files.

                     Don't print ELF details.

                     Don't check text encodings.

                     Don't consult magic files.

                     Don't examine tar files.

                     Don't check for various types of text files.

                     Don't look for known tokens inside ascii files.

                     Don't examine JSON files.

                     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 num‐
     ber (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 con‐
     tents 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 data‐
     base 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

     The MAGIC_PARAM_PHNUM_MAX parameter controls how many ELF program sec‐
     tions 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 data‐
     /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

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.  Informa‐
     tion about the project can be found at
     If you have a bug report for this manual page, see
     ⟨⟩.  This page was obtained from the
     project's upstream Git read-only mirror of the CVS repository
     ⟨⟩ on 2020-09-18.  (At that time, the
     date of the most recent commit that was found in the repository was
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BSD                             June 8, 2019                             BSD