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Dd June 16, 2023
Dt LIBMAGIC 3
Os
Sh NAME
Nm magic_open ,
Nm magic_close ,
Nm magic_error ,
Nm magic_errno ,
Nm magic_descriptor ,
Nm magic_file ,
Nm magic_buffer ,
Nm magic_getflags ,
Nm magic_setflags ,
Nm magic_check ,
Nm magic_compile ,
Nm magic_list ,
Nm magic_load ,
Nm magic_load_buffers ,
Nm magic_setparam ,
Nm magic_getparam ,
Nm magic_version
Nd Magic number recognition library
Sh LIBRARY
Lb libmagic
Sh SYNOPSIS
In magic.h
Ft magic_t
Fn magic_open "int flags"
Ft void
Fn magic_close "magic_t cookie"
Ft const char *
Fn magic_error "magic_t cookie"
Ft int
Fn magic_errno "magic_t cookie"
Ft const char *
Fn magic_descriptor "magic_t cookie" "int fd"
Ft const char *
Fn magic_file "magic_t cookie" "const char *filename"
Ft const char *
Fn magic_buffer "magic_t cookie" "const void *buffer" "size_t length"
Ft int
Fn magic_getflags "magic_t cookie"
Ft int
Fn magic_setflags "magic_t cookie" "int flags"
Ft int
Fn magic_check "magic_t cookie" "const char *filename"
Ft int
Fn magic_compile "magic_t cookie" "const char *filename"
Ft int
Fn magic_list "magic_t cookie" "const char *filename"
Ft int
Fn magic_load "magic_t cookie" "const char *filename"
Ft int
Fn magic_load_buffers "magic_t cookie" "void **buffers" "size_t *sizes" "size_t nbuffers"
Ft int
Fn magic_getparam "magic_t cookie" "int param" "void *value"
Ft int
Fn magic_setparam "magic_t cookie" "int param" "const void *value"
Ft int
Fn magic_version "void"
Ft const char *
Fn magic_getpath "const char *magicfile" "int action"
Sh DESCRIPTION
These functions
operate on the magic database file
which is described
in
Xr magic 5 .
Pp
The function
Fn magic_open
creates a magic cookie pointer and returns it.
It returns
Dv NULL
if there was an error allocating the magic cookie.
The
Ar flags
argument specifies how the other magic functions should behave:
Bl -tag -width MAGIC_COMPRESS
It Dv MAGIC_NONE
No special handling.
It Dv MAGIC_DEBUG
Print debugging messages to stderr.
It Dv MAGIC_SYMLINK
If the file queried is a symlink, follow it.
It Dv MAGIC_COMPRESS
If the file is compressed, unpack it and look at the contents.
It Dv MAGIC_DEVICES
If the file is a block or character special device, then open the device
and try to look in its contents.
It Dv MAGIC_MIME_TYPE
Return a MIME type string, instead of a textual description.
It Dv MAGIC_MIME_ENCODING
Return a MIME encoding, instead of a textual description.
It Dv MAGIC_MIME
A shorthand for MAGIC_MIME_TYPE | MAGIC_MIME_ENCODING.
It Dv MAGIC_CONTINUE
Return all matches, not just the first.
It Dv MAGIC_CHECK
Check the magic database for consistency and print warnings to stderr.
It Dv MAGIC_PRESERVE_ATIME
On systems that support
Xr utime 3
or
Xr utimes 2 ,
attempt to preserve the access time of files analysed.
It Dv MAGIC_RAW
Don't translate unprintable characters to a \eooo octal representation.
It Dv 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.
It Dv MAGIC_APPLE
Return the Apple creator and type.
It Dv MAGIC_EXTENSION
Return a slash-separated list of extensions for this file type.
It Dv MAGIC_COMPRESS_TRANSP
Don't report on compression, only report about the uncompressed data.
It Dv MAGIC_NO_CHECK_APPTYPE
Don't check for
Dv EMX
application type (only on EMX).
It Dv MAGIC_NO_COMPRESS_FORK
Don't allow decompressors that use fork.
It Dv MAGIC_NO_CHECK_CDF
Don't get extra information on MS Composite Document Files.
It Dv MAGIC_NO_CHECK_COMPRESS
Don't look inside compressed files.
It Dv MAGIC_NO_CHECK_ELF
Don't print ELF details.
It Dv MAGIC_NO_CHECK_ENCODING
Don't check text encodings.
It Dv MAGIC_NO_CHECK_SOFT
Don't consult magic files.
It Dv MAGIC_NO_CHECK_TAR
Don't examine tar files.
It Dv MAGIC_NO_CHECK_TEXT
Don't check for various types of text files.
It Dv MAGIC_NO_CHECK_TOKENS
Don't look for known tokens inside ascii files.
It Dv MAGIC_NO_CHECK_JSON
Don't examine JSON files.
It Dv MAGIC_NO_CHECK_CSV
Don't examine CSV files.
It Dv MAGIC_NO_CHECK_SIMH
Don't examine SIMH tape files.
El
Pp
The
Fn magic_close
function closes the
Xr magic 5
database and deallocates any resources used.
Pp
The
Fn magic_error
function returns a textual explanation of the last error, or
Dv NULL
if there was no error.
Pp
The
Fn magic_errno
function returns the last operating system error number
Pq Xr errno 2
that was encountered by a system call.
Pp
The
Fn magic_file
function returns a textual description of the contents of the
Ar filename
argument, or
Dv NULL
if an error occurred.
If the
Ar filename
is
Dv NULL ,
then stdin is used.
Pp
The
Fn magic_descriptor
function returns a textual description of the contents of the
Ar fd
argument, or
Dv NULL
if an error occurred.
Pp
The
Fn magic_buffer
function returns a textual description of the contents of the
Ar buffer
argument with
Ar length
bytes size.
Pp
The
Fn magic_getflags
functions returns a value representing current
Ar flags
set.
Pp
The
Fn magic_setflags
function sets the
Ar flags
described above.
Note that using both MIME flags together can also
return extra information on the charset.
Pp
The
Fn magic_check
function can be used to check the validity of entries in the colon
separated database files passed in as
Ar filename ,
or
Dv NULL
for the default database.
It returns 0 on success and \-1 on failure.
Pp
The
Fn magic_compile
function can be used to compile the colon
separated list of database files passed in as
Ar filename ,
or
Dv NULL
for the default database.
It returns 0 on success and \-1 on failure.
The compiled files created are named from the
Xr basename 1
of each file argument with
Dq .mgc
appended to it.
Pp
The
Fn 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
Fa filename
argument which is a colon separated list of database files, or
Dv NULL
for the default database.
Pp
The
Fn magic_load
function must be used to load the colon
separated list of database files passed in as
Ar filename ,
or
Dv NULL
for the default database file before any magic queries can performed.
Pp
The default database file is named by the MAGIC environment variable.
If that variable is not set, the default database file name is
Pa /usr/share/misc/magic .
Fn magic_load
adds
Dq .mgc
to the database filename as appropriate.
Pp
The
Fn magic_load_buffers
function takes an array of size
Fa nbuffers
of
Fa buffers
with a respective size for each in the array of
Fa 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.
Pp
The
Fn magic_getparam
and
Fn magic_setparam
allow getting and setting various limits related to the magic
library.
Bl -column "MAGIC_PARAM_ELF_PHNUM_MAX" "size_t" "Default" -offset indent
It Sy "Parameter" Ta Sy "Type" Ta Sy "Default"
It Li MAGIC_PARAM_INDIR_MAX Ta size_t Ta 15
It Li MAGIC_PARAM_NAME_MAX Ta size_t Ta 30
It Li MAGIC_PARAM_ELF_NOTES_MAX Ta size_t Ta 256
It Li MAGIC_PARAM_ELF_PHNUM_MAX Ta size_t Ta 128
It Li MAGIC_PARAM_ELF_SHNUM_MAX Ta size_t Ta 32768
It Li MAGIC_PARAM_REGEX_MAX Ta size_t Ta 8192
It Li MAGIC_PARAM_BYTES_MAX Ta size_t Ta 1048576
El
Pp
The
Dv MAGIC_PARAM_INDIR_RECURSION
parameter controls how many levels of recursion will be followed for
indirect magic entries.
Pp
The
Dv MAGIC_PARAM_NAME_RECURSION
parameter controls how many levels of recursion will be followed for
for name/use calls.
Pp
The
Dv MAGIC_PARAM_NAME_MAX
parameter controls the maximum number of calls for name/use.
Pp
The
Dv MAGIC_PARAM_NOTES_MAX
parameter controls how many ELF notes will be processed.
Pp
The
Dv MAGIC_PARAM_PHNUM_MAX
parameter controls how many ELF program sections will be processed.
Pp
The
Dv MAGIC_PARAM_SHNUM_MAX
parameter controls how many ELF sections will be processed.
Pp
The
Fn magic_version
command returns the version number of this library which is compiled into
the shared library using the constant
Dv MAGIC_VERSION
from
In 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.
Pp
The
Fn magic_getpath
command returns the colon separated list of magic database locations.
If the
Fa filename
is non-NULL, then it is returned.
Otherwise, if the
Dv MAGIC
environment variable is defined, then it is returned.
Otherwise, if
Fa 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.
Sh RETURN VALUES
The function
Fn magic_open
returns a magic cookie on success and
Dv NULL
on failure setting errno to an appropriate value.
It will set errno to
Er EINVAL
if an unsupported value for flags was given.
The
Fn magic_list ,
Fn magic_load ,
Fn magic_compile ,
and
Fn magic_check
functions return 0 on success and \-1 on failure.
The
Fn magic_buffer ,
Fn magic_getpath ,
and
Fn magic_file ,
functions return a string on success and
Dv NULL
on failure.
The
Fn magic_error
function returns a textual description of the errors of the above
functions, or
Dv NULL
if there was no error.
The
Fn magic_version
always returns the version number of the library.
Finally,
Fn magic_setflags
returns \-1 on systems that don't support
Xr utime 3 ,
or
Xr utimes 2
when
Dv MAGIC_PRESERVE_ATIME
is set.
Sh FILES
Bl -tag -width /usr/share/misc/magic.mgc -compact
It Pa /usr/share/misc/magic
The non-compiled default magic database.
It Pa /usr/share/misc/magic.mgc
The compiled default magic database.
El
Sh SEE ALSO
Xr file 1 ,
Xr magic 5
Sh BUGS
The results from
Fn magic_buffer
and
Fn magic_file
where the buffer and the file contain the same data
can produce different results, because in the
Fn magic_file
case, the program can
Xr lseek 2
and
Xr stat 2
the file descriptor.
Sh AUTHORS
An M\(oans Rullg\(oard
Initial libmagic implementation, and configuration.
An Christos Zoulas
API cleanup, error code and allocation handling.

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