minix/external/bsd/file/dist/doc/libmagic.3

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.Dd October 6, 2008
.Dt LIBMAGIC 3
.Os
.Sh NAME
.Nm magic_open ,
.Nm magic_close ,
.Nm magic_error ,
.Nm magic_file ,
.Nm magic_buffer ,
.Nm magic_setflags ,
.Nm magic_check ,
.Nm magic_compile ,
.Nm magic_load
.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_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_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_load "magic_t cookie" "const char *filename"
.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_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 analyzed.
.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_NO_CHECK_APPTYPE
Check for
.Dv EMX
application type (only on EMX).
.It Dv MAGIC_NO_CHECK_ASCII
Check for various types of ascii files.
.It Dv MAGIC_NO_CHECK_COMPRESS
Don't look for, or inside compressed files.
.It Dv MAGIC_NO_CHECK_ELF
Don't print elf details.
.It Dv MAGIC_NO_CHECK_FORTRAN
Don't look for fortran sequences inside ascii files.
.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_TOKENS
Don't look for known tokens inside ascii files.
.It Dv MAGIC_NO_CHECK_TROFF
Don't look for troff sequences inside ascii 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_buffer
function returns a textual description of the contents of the
.Ar buffer
argument with
.Ar length
bytes size.
.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 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_load
function must be used to load the 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.
.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_load ,
.Fn magic_compile ,
and
.Fn magic_check
functions return 0 on success and \-1 on failure.
The
.Fn magic_file ,
and
.Fn magic_buffer
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.
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 AUTHORS
.An M\(oans Rullg\(oard
Initial libmagic implementation, and configuration.
.An Christos Zoulas
API cleanup, error code and allocation handling.