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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | FILES | SEE ALSO | BUGS | AUTHORS | COLOPHON |
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LIBMAGIC(3) Library Functions Manual LIBMAGIC(3)
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
Magic Number Recognition Library (libmagic, -lmagic)
<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)
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 7340032
MAGIC_PARAM_ENCODING_MAX size_t 1048576
MAGIC_PARAM_ELF_SHSIZE_MAX size_t 134217728
MAGIC_PARAM_MAGWARN_MAX size_t 64
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_PARAM_REGEX_MAX parameter controls the maximum length
for regex searches.
The MAGIC_PARAM_BYTES_MAX parameter controls the maximum number of
bytes to look inside a file.
The MAGIC_PARAM_ENCODING_MAX parameter controls the maximum number
of bytes to scan for encoding detection.
The MAGIC_PARAM_ELF_SHSIZE_MAX parameter controls the maximum
number of bytes in an elf section.
The MAGIC_PARAM_MAGWARN_MAX parameter controls the maximum number
of warnings to tolerate in a magic file.
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.
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.
/usr/local/share/misc/magic The non-compiled default magic
database.
/usr/local/share/misc/magic.mgc The compiled default magic
database.
file(1), magic(4)
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.
Måns Rullgård Initial libmagic implementation, and configuration.
Christos Zoulas API cleanup, error code and allocation handling.
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 2025-08-11.
(At that time, the date of the most recent commit that was found
in the repository was 2025-07-23.) 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
GNU December 29, 2023 LIBMAGIC(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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