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.TH MAGIC 5 "Public Domain" .\"
.\" @(#)$Id: magic.5,v 1.8 1997/11/04 03:56:56 steve Exp $
.\"
.\" install as magic.4 on USG, magic.5 on V7 or Berkeley systems. .\" install as magic.4 on USG, magic.5 on V7 or Berkeley systems.
.SH NAME .\"
magic \- file command's magic number file .Dd September 3, 1994
.SH DESCRIPTION .Dt MAGIC 5
.Os "Public Domain"
.Sh NAME
.Nm magic
.Nd file command's magic number file
.Sh DESCRIPTION
This manual page documents the format of the magic file as This manual page documents the format of the magic file as
used by the used by the
.BR file (1) .Xr file 1
command, version 3.22. The command, version 3.22. The
.B file .Nm file
command identifies the type of a file using, command identifies the type of a file using,
among other tests, among other tests,
a test for whether the file begins with a certain a test for whether the file begins with a certain
.IR "magic number" . .Em "magic number" .
The file The file
.I /usr/share/misc/magic .Pa /usr/share/misc/magic
specifies what magic numbers are to be tested for, specifies what magic numbers are to be tested for,
what message to print if a particular magic number is found, what message to print if a particular magic number is found,
and additional information to extract from the file. and additional information to extract from the file.
.PP .Pp
Each line of the file specifies a test to be performed. Each line of the file specifies a test to be performed.
A test compares the data starting at a particular offset A test compares the data starting at a particular offset
in the file with a 1-byte, 2-byte, or 4-byte numeric value or in the file with a 1-byte, 2-byte, or 4-byte numeric value or
a string. If the test succeeds, a message is printed. a string. If the test succeeds, a message is printed.
The line consists of the following fields: The line consists of the following fields:
.IP offset \w'message'u+2n .Bl -tag -width indent
.It offset
A number specifying the offset, in bytes, into the file of the data A number specifying the offset, in bytes, into the file of the data
which is to be tested. which is to be tested.
.IP type .It type
The type of the data to be tested. The possible values are: The type of the data to be tested. The possible values are:
.RS .Bl -tag -width indent
.IP byte \w'message'u+2n .It byte
A one-byte value. A one-byte value.
.IP short .It short
A two-byte value (on most systems) in this machine's native byte order. A two-byte value (on most systems) in this machine's native byte order.
.IP long .It long
A four-byte value (on most systems) in this machine's native byte order. A four-byte value (on most systems) in this machine's native byte order.
.IP string .It string
A string of bytes. A string of bytes.
.IP date .It date
A four-byte value interpreted as a unix date. A four-byte value interpreted as a unix date.
.IP beshort .It beshort
A two-byte value (on most systems) in big-endian byte order. A two-byte value (on most systems) in big-endian byte order.
.IP belong .It belong
A four-byte value (on most systems) in big-endian byte order. A four-byte value (on most systems) in big-endian byte order.
.IP bedate .It bedate
A four-byte value (on most systems) in big-endian byte order, A four-byte value (on most systems) in big-endian byte order,
interpreted as a unix date. interpreted as a unix date.
.IP leshort .It leshort
A two-byte value (on most systems) in little-endian byte order. A two-byte value (on most systems) in little-endian byte order.
.IP lelong .It lelong
A four-byte value (on most systems) in little-endian byte order. A four-byte value (on most systems) in little-endian byte order.
.IP ledate .It ledate
A four-byte value (on most systems) in little-endian byte order, A four-byte value (on most systems) in little-endian byte order,
interpreted as a unix date. interpreted as a unix date.
.RE .El
.PP .El
.Pp
The numeric types may optionally be followed by The numeric types may optionally be followed by
.B & .Em &
and a numeric value, and a numeric value,
to specify that the value is to be AND'ed with the to specify that the value is to be AND'ed with the
numeric value before any comparisons are done. Prepending a numeric value before any comparisons are done. Prepending a
.B u .Em u
to the type indicates that ordered comparisons should be unsigned. to the type indicates that ordered comparisons should be unsigned.
.IP test .Bl -tag -width indent
.It test
The value to be compared with the value from the file. If the type is The value to be compared with the value from the file. If the type is
numeric, this value numeric, this value
is specified in C form; if it is a string, it is specified as a C string is specified in C form; if it is a string, it is specified as a C string
with the usual escapes permitted (e.g. \en for new-line). with the usual escapes permitted (e.g. \en for new-line).
.IP .It ""
Numeric values Numeric values
may be preceded by a character indicating the operation to be performed. may be preceded by a character indicating the operation to be performed.
It may be It may be
.BR = , .Em = ,
to specify that the value from the file must equal the specified value, to specify that the value from the file must equal the specified value,
.BR < , .Em < ,
to specify that the value from the file must be less than the specified to specify that the value from the file must be less than the specified
value, value,
.BR > , .Em > ,
to specify that the value from the file must be greater than the specified to specify that the value from the file must be greater than the specified
value, value,
.BR & , .Em & ,
to specify that the value from the file must have set all of the bits to specify that the value from the file must have set all of the bits
that are set in the specified value, that are set in the specified value,
.BR ^ , .Em ^ ,
to specify that the value from the file must have clear any of the bits to specify that the value from the file must have clear any of the bits
that are set in the specified value, or that are set in the specified value, or
.BR x , .Em x ,
to specify that any value will match. If the character is omitted, to specify that any value will match. If the character is omitted,
it is assumed to be it is assumed to be
.BR = . .Em = .
.IP .It ""
Numeric values are specified in C form; e.g. Numeric values are specified in C form; e.g.
.B 13 .Em 13
is decimal, is decimal,
.B 013 .Em 013
is octal, and is octal, and
.B 0x13 .Em 0x13
is hexadecimal. is hexadecimal.
.IP .It ""
For string values, the byte string from the For string values, the byte string from the
file must match the specified byte string. file must match the specified byte string.
The operators The operators
.BR = , .Em = ,
.B < .Em <
and and
.B > .Em >
(but not (but not
.BR & ) .Em & )
can be applied to strings. can be applied to strings.
The length used for matching is that of the string argument The length used for matching is that of the string argument
in the magic file. This means that a line can match any string, and in the magic file. This means that a line can match any string, and
then presumably print that string, by doing then presumably print that string, by doing
.B >\e0 .Em >\e0
(because all strings are greater than the null string). (because all strings are greater than the null string).
.IP message .It message
The message to be printed if the comparison succeeds. If the string The message to be printed if the comparison succeeds. If the string
contains a contains a
.BR printf (3S) .Xr printf 3
format specification, the value from the file (with any specified masking format specification, the value from the file (with any specified masking
performed) is printed using the message as the format string. performed) is printed using the message as the format string.
.PP .El
.Pp
Some file formats contain additional information which is to be printed Some file formats contain additional information which is to be printed
along with the file type. A line which begins with the character along with the file type. A line which begins with the character
.B > .Em >
indicates additional tests and messages to be printed. The number of indicates additional tests and messages to be printed. The number of
.B > .Em >
on the line indicates the level of the test; a line with no on the line indicates the level of the test; a line with no
.B > .Em >
at the beginning is considered to be at level 0. at the beginning is considered to be at level 0.
Each line at level Each line at level
.IB n \(pl1 .Em n+1
is under the control of the line at level is under the control of the line at level
.IB n .Em n
most closely preceding it in the magic file. most closely preceding it in the magic file.
If the test on a line at level If the test on a line at level
.I n .Em n
succeeds, the tests specified in all the subsequent lines at level succeeds, the tests specified in all the subsequent lines at level
.IB n \(pl1 .Em n+1
are performed, and the messages printed if the tests succeed. The next are performed, and the messages printed if the tests succeed. The next
line at level line at level
.I n .Em n
terminates this. terminates this.
If the first character following the last If the first character following the last
.B > .Em >
is a is a
.B ( .Em (
then the string after the parenthesis is interpreted as an indirect offset. then the string after the parenthesis is interpreted as an indirect offset.
That means that the number after the parenthesis is used as an offset in That means that the number after the parenthesis is used as an offset in
the file. The value at that offset is read, and is used again as an offset the file. The value at that offset is read, and is used again as an offset
in the file. Indirect offsets are of the form: in the file. Indirect offsets are of the form:
.BI ( x [.[bsl]][+-][ y ]). .Em (x[.[bsl]][+-][y]) .
The value of The value of
.I x .Em x
is used as an offset in the file. A byte, short or long is read at that offset is used as an offset in the file. A byte, short or long is read at that offset
depending on the depending on the
.B [bsl] .Em [bsl]
type specifier. To that number the value of type specifier. To that number the value of
.I y .Em y
is added and the result is used as an offset in the file. The default type is added and the result is used as an offset in the file. The default type
if one is not specified is long. if one is not specified is long.
.PP .Pp
Sometimes you do not know the exact offset as this depends on the length of Sometimes you do not know the exact offset as this depends on the length of
preceding fields. You can specify an offset relative to the end of the preceding fields. You can specify an offset relative to the end of the
last uplevel field (of course this may only be done for sublevel tests, i.e. last uplevel field (of course this may only be done for sublevel tests, i.e.
test beginning with test beginning with
.B > .Em > Ns ).
). Such a relative offset is specified using Such a relative offset is specified using
.B & .Em &
as a prefix to the offset. as a prefix to the offset.
.SH BUGS .Sh BUGS
The formats The formats
.IR long , .Em long ,
.IR belong , .Em belong ,
.IR lelong , .Em lelong ,
.IR short , .Em short ,
.IR beshort , .Em beshort ,
.IR leshort , .Em leshort ,
.IR date , .Em date ,
.IR bedate , .Em bedate ,
and and
.I ledate .Em ledate
are system-dependent; perhaps they should be specified as a number are system-dependent; perhaps they should be specified as a number
of bytes (2B, 4B, etc), of bytes (2B, 4B, etc),
since the files being recognized typically come from since the files being recognized typically come from
a system on which the lengths are invariant. a system on which the lengths are invariant.
.PP .Pp
There is (currently) no support for specified-endian data to be used in There is (currently) no support for specified-endian data to be used in
indirect offsets. indirect offsets.
.SH SEE ALSO .Sh SEE ALSO
.BR file (1) .Xr file 1
\- the command that reads this file.
.\" .\"
.\" From: guy@sun.uucp (Guy Harris) .\" From: guy@sun.uucp (Guy Harris)
.\" Newsgroups: net.bugs.usg .\" Newsgroups: net.bugs.usg
@ -203,4 +213,3 @@ indirect offsets.
.\" the changes I posted to the S5R2 version. .\" the changes I posted to the S5R2 version.
.\" .\"
.\" Modified for Ian Darwin's version of the file command. .\" Modified for Ian Darwin's version of the file command.
.\" @(#)$Id: magic.5,v 1.7 1997/03/18 19:37:20 mpp Exp $