libmagic man page

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

Library

Magic Number Recognition Library (libmagic, -lmagic)

Synopsis

#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_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

These functions operate on the magic database file which is described in magic(5).

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.

The magic_close() function closes the magic(5) 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_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/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

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

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

See Also

file(1), magic(5)

Authors

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

Info

September 11, 2015