Provided by: tcl8.6-doc_8.6.1-4ubuntu1_all bug

NAME

       binary - Insert and extract fields from binary strings

SYNOPSIS

       binary decode format ?-option value ...? databinary encode format ?-option value ...? databinary format formatString ?arg arg ...?
       binary scan string formatString ?varName varName ...?
_________________________________________________________________

DESCRIPTION

       This  command  provides  facilities  for  manipulating binary data.  The subcommand binary
       format creates a binary string from normal Tcl values.  For example, given the  values  16
       and  22,  on a 32-bit architecture, it might produce an 8-byte binary string consisting of
       two 4-byte integers, one for each of the numbers.  The subcommand binary  scan,  does  the
       opposite:  it  extracts  data  from  a binary string and returns it as ordinary Tcl string
       values.  The binary encode and binary decode subcommands convert binary data  to  or  from │
       string encodings such as base64 (used in MIME messages for example).

       Note that other operations on binary data, such as taking a subsequence of it, getting its
       length, or reinterpreting it as a string in some encoding, are done by other Tcl  commands
       (respectively  string range, string length and encoding convertfrom in the example cases).
       A binary string in Tcl is merely one where all the characters it contains are in the range
       \u0000-\u00FF.

BINARY ENCODE AND DECODE

       When  encoding binary data as a readable string, the starting binary data is passed to the │
       binary encode command, together with the name of the encoding to  use  and  any  encoding- │
       specific options desired. Data which has been encoded can be converted back to binary form │
       using binary decode. The following formats and options are supported.                      │

       base64                                                                                     │
              The base64 binary encoding is commonly used in mail messages and XML documents, and │
              uses  mostly  upper  and  lower  case letters and digits. It has the distinction of │
              being able to be rewrapped arbitrarily without losing information.                  │

              During encoding, the following options are supported:                               │

              -maxlen length                                                                      │
                     Indicates that the output should be split into lines of no more than  length │
                     characters. By default, lines are not split.                                 │

              -wrapchar character                                                                 │
                     Indicates  that,  when  lines  are  split  because  of  the  -maxlen option, │
                     character should be used to separate lines. By default, this  is  a  newline │
                     character, “\n”.                                                             │

              During decoding, the following options are supported:                               │

              -strict                                                                             │
                     Instructs  the  decoder  to  throw  an  error  if  it  encounters whitespace │
                     characters. Otherwise it ignores them.                                       │

       hex                                                                                        │
              The hex binary encoding converts each byte to a pair of hexadecimal digits in  big- │
              endian form.                                                                        │

              No  options  are  supported during encoding. During decoding, the following options │
              are supported:                                                                      │

              -strict                                                                             │
                     Instructs the  decoder  to  throw  an  error  if  it  encounters  whitespace │
                     characters. Otherwise it ignores them.                                       │

       uuencode                                                                                   │
              The  uuencode  binary  encoding used to be common for transfer of data between Unix │
              systems and on  USENET,  but  is  less  common  these  days,  having  been  largely │
              superseded by the base64 binary encoding.                                           │

              During  encoding,  the  following  options  are supported (though changing them may │
              produce files that other implementations of decoders cannot process):               │

              -maxlen length                                                                      │
                     Indicates that the output should be split into lines of no more than  length │
                     characters.  By  default, lines are split every 61 characters, and this must │
                     be in the range 3 to 85 due to limitations in the encoding.                  │

              -wrapchar character                                                                 │
                     Indicates that,  when  lines  are  split  because  of  the  -maxlen  option, │
                     character  should  be  used to separate lines. By default, this is a newline │
                     character, “\n”.                                                             │

              During decoding, the following options are supported:                               │

              -strict                                                                             │
                     Instructs the  decoder  to  throw  an  error  if  it  encounters  unexpected │
                     whitespace characters. Otherwise it ignores them.                            │

              Note  that  neither the encoder nor the decoder handle the header and footer of the │
              uuencode format.                                                                    │

BINARY FORMAT

       The binary format command generates a binary string  whose  layout  is  specified  by  the
       formatString  and whose contents come from the additional arguments.  The resulting binary
       value is returned.

       The formatString consists of a sequence of zero or more field specifiers separated by zero
       or  more  spaces.  Each field specifier is a single type character followed by an optional
       flag character followed by an optional numeric count.  Most field specifiers  consume  one
       argument  to obtain the value to be formatted.  The type character specifies how the value
       is to be formatted.  The count typically indicates how many items of  the  specified  type
       are  taken  from the value.  If present, the count is a non-negative decimal integer or *,
       which normally indicates that all of the items in the value are to be used.  If the number
       of  arguments  does  not  match  the  number  of  fields in the format string that consume
       arguments, then an error is generated. The flag character is ignored for binary format.

       Here is a small example to clarify the relation  between  the  field  specifiers  and  the
       arguments:
              binary format d3d {1.0 2.0 3.0 4.0} 0.1

       The  first  argument  is  a  list  of  four numbers, but because of the count of 3 for the
       associated field specifier, only the first three will be  used.  The  second  argument  is
       associated  with the second field specifier. The resulting binary string contains the four
       numbers 1.0, 2.0, 3.0 and 0.1.

       Each type-count pair moves an imaginary cursor through the binary data, storing  bytes  at
       the  current  position  and  advancing the cursor to just after the last byte stored.  The
       cursor is initially at position 0 at the beginning of the data.  The type may be  any  one
       of the following characters:

       a    Stores  a byte string of length count in the output string.  Every character is taken
            as modulo 256 (i.e. the low byte of every  character  is  used,  and  the  high  byte
            discarded)  so  when  storing  character  strings  not  wholly  expressible using the
            characters \u0000-\u00ff, the encoding convertto command  should  be  used  first  to
            change  the  string into an external representation if this truncation is not desired
            (i.e. if the characters are not part of the ISO 8859-1 character set.)   If  arg  has
            fewer than count bytes, then additional zero bytes are used to pad out the field.  If
            arg is longer than the specified length, the extra characters will  be  ignored.   If
            count  is  *,  then  all of the bytes in arg will be formatted.  If count is omitted,
            then one character will be formatted.  For example,
                   binary format a7a*a alpha bravo charlie
            will return a string equivalent to alpha\000\000bravoc,
                   binary format a* [encoding convertto utf-8 \u20ac]
            will return a string equivalent to \342\202\254 (which is the UTF-8 byte sequence for
            a Euro-currency character) and
                   binary format a* [encoding convertto iso8859-15 \u20ac]
            will return a string equivalent to \244 (which is the ISO 8859-15 byte sequence for a
            Euro-currency character). Contrast these last two with:
                   binary format a* \u20ac
            which returns a string equivalent to \254 (i.e. \xac) by truncating the high-bits  of
            the character, and which is probably not what is desired.

       A    This  form is the same as a except that spaces are used for padding instead of nulls.
            For example,
                   binary format A6A*A alpha bravo charlie
            will return alpha bravoc.

       b    Stores a string of count binary digits in low-to-high order within each byte  in  the
            output  string.   Arg  must  contain a sequence of 1 and 0 characters.  The resulting
            bytes are emitted in first to last order with the bits being formatted in low-to-high
            order  within each byte.  If arg has fewer than count digits, then zeros will be used
            for the remaining bits.  If arg has more than the specified  number  of  digits,  the
            extra  digits  will be ignored.  If count is *, then all of the digits in arg will be
            formatted.  If count is omitted, then one digit will be formatted.  If the number  of
            bits  formatted  does not end at a byte boundary, the remaining bits of the last byte
            will be zeros.  For example,
                   binary format b5b* 11100 111000011010
            will return a string equivalent to \x07\x87\x05.

       B    This form is the same as b except that the  bits  are  stored  in  high-to-low  order
            within each byte.  For example,
                   binary format B5B* 11100 111000011010
            will return a string equivalent to \xe0\xe1\xa0.

       H    Stores  a  string  of count hexadecimal digits in high-to-low within each byte in the
            output  string.   Arg  must  contain  a   sequence   of   characters   in   the   set
            “0123456789abcdefABCDEF”.   The  resulting  bytes  are emitted in first to last order
            with the hex digits being formatted in high-to-low order within each  byte.   If  arg
            has  fewer  than  count digits, then zeros will be used for the remaining digits.  If
            arg has more than the specified number of digits, the extra digits will  be  ignored.
            If count is *, then all of the digits in arg will be formatted.  If count is omitted,
            then one digit will be formatted.  If the number of digits formatted does not end  at
            a byte boundary, the remaining bits of the last byte will be zeros.  For example,
                   binary format H3H*H2 ab DEF 987
            will return a string equivalent to \xab\x00\xde\xf0\x98.

       h    This  form  is  the  same as H except that the digits are stored in low-to-high order
            within each byte. This is seldom required. For example,
                   binary format h3h*h2 AB def 987
            will return a string equivalent to \xba\x00\xed\x0f\x89.

       c    Stores one or more 8-bit integer values  in  the  output  string.   If  no  count  is
            specified, then arg must consist of an integer value. If count is specified, arg must
            consist of a list containing at least that many integers. The  low-order  8  bits  of
            each  integer  are stored as a one-byte value at the cursor position.  If count is *,
            then all of the integers in the list are formatted. If the number of elements in  the
            list is greater than count, then the extra elements are ignored.  For example,
                   binary format c3cc* {3 -3 128 1} 260 {2 5}
            will return a string equivalent to \x03\xfd\x80\x04\x02\x05, whereas
                   binary format c {2 5}
            will generate an error.

       s    This  form  is  the  same  as  c except that it stores one or more 16-bit integers in
            little-endian byte order in the output string.  The low-order 16-bits of each integer
            are stored as a two-byte value at the cursor position with the least significant byte
            stored first.  For example,
                   binary format s3 {3 -3 258 1}
            will return a string equivalent to \x03\x00\xfd\xff\x02\x01.

       S    This form is the same as s except that it stores one or more 16-bit integers in  big-
            endian byte order in the output string.  For example,
                   binary format S3 {3 -3 258 1}
            will return a string equivalent to \x00\x03\xff\xfd\x01\x02.

       t    This form (mnemonically tiny) is the same as s and S except that it stores the 16-bit
            integers in the output string in the native byte order of the machine where  the  Tcl
            script  is running.  To determine what the native byte order of the machine is, refer
            to the byteOrder element of the tcl_platform array.

       i    This form is the same as c except that it stores  one  or  more  32-bit  integers  in
            little-endian byte order in the output string.  The low-order 32-bits of each integer
            are stored as a four-byte value at the cursor position  with  the  least  significant
            byte stored first.  For example,
                   binary format i3 {3 -3 65536 1}
            will return a string equivalent to \x03\x00\x00\x00\xfd\xff\xff\xff\x00\x00\x01\x00

       I    This  form  is  the  same  as  i except that it stores one or more one or more 32-bit
            integers in big-endian byte order in the output string.  For example,
                   binary format I3 {3 -3 65536 1}
            will return a string equivalent to \x00\x00\x00\x03\xff\xff\xff\xfd\x00\x01\x00\x00

       n    This form (mnemonically number or normal) is the same as  i  and  I  except  that  it
            stores  the  32-bit  integers  in  the  output string in the native byte order of the
            machine where the Tcl script is running.  To determine what the native byte order  of
            the machine is, refer to the byteOrder element of the tcl_platform array.

       w    This  form  is  the  same  as  c except that it stores one or more 64-bit integers in
            little-endian byte order in the output string.  The low-order 64-bits of each integer
            are  stored  as an eight-byte value at the cursor position with the least significant
            byte stored first.  For example,
                   binary format w 7810179016327718216
            will return the string HelloTcl

       W    This form is the same as w except that it stores one  or  more  one  or  more  64-bit
            integers in big-endian byte order in the output string.  For example,
                   binary format Wc 4785469626960341345 110
            will return the string BigEndian

       m    This form (mnemonically the mirror of w) is the same as w and W except that it stores
            the 64-bit integers in the output string in the native  byte  order  of  the  machine
            where  the  Tcl  script  is  running.  To determine what the native byte order of the
            machine is, refer to the byteOrder element of the tcl_platform array.

       f    This form is the same as c except that it stores one or  more  one  or  more  single-
            precision floating point numbers in the machine's native representation in the output
            string.  This representation is not portable across architectures, so it  should  not
            be  used  to  communicate  floating  point numbers across the network.  The size of a
            floating point number may vary across architectures, so the number of bytes that  are
            generated may vary.  If the value overflows the machine's native representation, then
            the value of FLT_MAX as defined by the system will be used instead.  Because Tcl uses
            double-precision  floating  point  numbers  internally,  there  may  be  some loss of
            precision in the conversion to single-precision.  For example, on  a  Windows  system
            running on an Intel Pentium processor,
                   binary format f2 {1.6 3.4}
            will return a string equivalent to \xcd\xcc\xcc\x3f\x9a\x99\x59\x40.

       r    This  form  (mnemonically  real)  is  the same as f except that it stores the single-
            precision floating point  numbers  in  little-endian  order.   This  conversion  only
            produces  meaningful  output  when used on machines which use the IEEE floating point
            representation (very common, but not universal.)

       R    This form is the same as r except that it stores the single-precision floating  point
            numbers in big-endian order.

       d    This  form  is  the  same  as f except that it stores one or more one or more double-
            precision floating point numbers in the machine's native representation in the output
            string.  For example, on a Windows system running on an Intel Pentium processor,
                   binary format d1 {1.6}
            will return a string equivalent to \x9a\x99\x99\x99\x99\x99\xf9\x3f.

       q    This  form  (mnemonically the mirror of d) is the same as d except that it stores the
            double-precision floating point numbers in little-endian order.  This conversion only
            produces  meaningful  output  when used on machines which use the IEEE floating point
            representation (very common, but not universal.)

       Q    This form is the same as q except that it stores the double-precision floating  point
            numbers in big-endian order.

       x    Stores  count null bytes in the output string.  If count is not specified, stores one
            null byte.  If count is *, generates  an  error.   This  type  does  not  consume  an
            argument.  For example,
                   binary format a3xa3x2a3 abc def ghi
            will return a string equivalent to abc\000def\000\000ghi.

       X    Moves  the  cursor back count bytes in the output string.  If count is * or is larger
            than the current cursor position, then the cursor is positioned at location 0 so that
            the  next  byte  stored  will  be  the  first byte in the result string.  If count is
            omitted then the cursor is moved back one  byte.   This  type  does  not  consume  an
            argument.  For example,
                   binary format a3X*a3X2a3 abc def ghi
            will return dghi.

       @    Moves  the  cursor  to the absolute location in the output string specified by count.
            Position 0 refers to the first byte in the output  string.   If  count  refers  to  a
            position  beyond  the  last byte stored so far, then null bytes will be placed in the
            uninitialized locations and the cursor will be placed at the specified location.   If
            count  is  *,  then  the cursor is moved to the current end of the output string.  If
            count is omitted, then an error will be generated.  This type  does  not  consume  an
            argument. For example,
                   binary format a5@2a1@*a3@10a1 abcde f ghi j
            will return abfdeghi\000\000j.

BINARY SCAN

       The  binary  scan  command  parses  fields  from  a binary string, returning the number of
       conversions performed.  String gives the input bytes to be parsed (one byte per character,
       and  characters not representable as a byte have their high bits chopped) and formatString
       indicates how to parse it.  Each varName gives the name of a variable;  when  a  field  is
       scanned from string the result is assigned to the corresponding variable.

       As  with  binary  format,  the  formatString  consists of a sequence of zero or more field
       specifiers separated by zero or more spaces.   Each  field  specifier  is  a  single  type
       character  followed  by  an optional flag character followed by an optional numeric count.
       Most field specifiers consume one argument to obtain the variable into which  the  scanned
       values  should  be  placed.   The  type  character  specifies how the binary data is to be
       interpreted.  The count typically indicates how many items of the specified type are taken
       from  the  data.   If  present,  the  count  is a non-negative decimal integer or *, which
       normally indicates that all of the remaining items in the data are to be used.   If  there
       are  not  enough bytes left after the current cursor position to satisfy the current field
       specifier, then the corresponding variable is  left  untouched  and  binary  scan  returns
       immediately with the number of variables that were set.  If there are not enough arguments
       for all of the fields in the format string  that  consume  arguments,  then  an  error  is
       generated.  The flag character “u” may be given to cause some types to be read as unsigned
       values. The flag is accepted for all field types but is ignored for non-integer fields.

       A similar example as  with  binary  format  should  explain  the  relation  between  field
       specifiers and arguments in case of the binary scan subcommand:
              binary scan $bytes s3s first second

       This  command  (provided the binary string in the variable bytes is long enough) assigns a
       list of three integers to the variable first and assigns a single value  to  the  variable
       second.   If  bytes contains fewer than 8 bytes (i.e. four 2-byte integers), no assignment
       to second will be made, and if bytes contains  fewer  than  6  bytes  (i.e.  three  2-byte
       integers), no assignment to first will be made.  Hence:
              puts [binary scan abcdefg s3s first second]
              puts $first
              puts $second
       will print (assuming neither variable is set previously):
              1
              25185 25699 26213
              can't read "second": no such variable

       It  is  important  to  note  that  the  c, s, and S (and i and I on 64bit systems) will be
       scanned into long data size values.  In doing this, values that have their  high  bit  set
       (0x80 for chars, 0x8000 for shorts, 0x80000000 for ints), will be sign extended.  Thus the
       following will occur:
              set signShort [binary format s1 0x8000]
              binary scan $signShort s1 val; # val == 0xFFFF8000
       If you require unsigned values you can include the “u” flag character following the  field
       type. For example, to read an unsigned short value:
              set signShort [binary format s1 0x8000]
              binary scan $signShort su1 val; # val == 0x00008000

       Each type-count pair moves an imaginary cursor through the binary data, reading bytes from
       the current position.  The cursor is initially at position 0 at the beginning of the data.
       The type may be any one of the following characters:

       a    The  data is a byte string of length count.  If count is *, then all of the remaining
            bytes in string will be scanned into the variable.  If count  is  omitted,  then  one
            byte  will  be scanned.  All bytes scanned will be interpreted as being characters in
            the range \u0000-\u00ff so the encoding convertfrom command will  be  needed  if  the
            string is not a binary string or a string encoded in ISO 8859-1.  For example,
                   binary scan abcde\000fghi a6a10 var1 var2
            will  return  1  with the string equivalent to abcde\000 stored in var1 and var2 left
            unmodified, and
                   binary scan \342\202\254 a* var1
                   set var2 [encoding convertfrom utf-8 $var1]
            will store a Euro-currency character in var2.

       A    This form is the same as a, except trailing blanks and nulls are  stripped  from  the
            scanned value before it is stored in the variable.  For example,
                   binary scan "abc efghi  \000" A* var1
            will return 1 with abc efghi stored in var1.

       b    The  data  is  turned  into  a  string  of  count  binary digits in low-to-high order
            represented as a sequence of “1” and “0” characters.  The data bytes are  scanned  in
            first  to last order with the bits being taken in low-to-high order within each byte.
            Any extra bits in the last byte are  ignored.   If  count  is  *,  then  all  of  the
            remaining  bits in string will be scanned.  If count is omitted, then one bit will be
            scanned.  For example,
                   binary scan \x07\x87\x05 b5b* var1 var2
            will return 2 with 11100 stored in var1 and 1110000110100000 stored in var2.

       B    This form is the same as b, except the bits are taken  in  high-to-low  order  within
            each byte.  For example,
                   binary scan \x70\x87\x05 B5B* var1 var2
            will return 2 with 01110 stored in var1 and 1000011100000101 stored in var2.

       H    The  data  is  turned  into a string of count hexadecimal digits in high-to-low order
            represented as a sequence of characters in  the  set  “0123456789abcdef”.   The  data
            bytes  are scanned in first to last order with the hex digits being taken in high-to-
            low order within each byte. Any extra bits in the last byte are ignored. If count  is
            *,  then  all  of  the  remaining  hex  digits in string will be scanned. If count is
            omitted, then one hex digit will be scanned. For example,
                   binary scan \x07\xC6\x05\x1f\x34 H3H* var1 var2
            will return 2 with 07c stored in var1 and 051f34 stored in var2.

       h    This form is the same as H, except the digits  are  taken  in  reverse  (low-to-high)
            order within each byte. For example,
                   binary scan \x07\x86\x05\x12\x34 h3h* var1 var2
            will return 2 with 706 stored in var1 and 502143 stored in var2.

            Note  that  most code that wishes to parse the hexadecimal digits from multiple bytes
            in order should use the H format.

       c    The data is turned into count 8-bit signed integers and stored in  the  corresponding
            variable  as a list. If count is *, then all of the remaining bytes in string will be
            scanned.  If count is omitted, then one 8-bit integer will be scanned.  For example,
                   binary scan \x07\x86\x05 c2c* var1 var2
            will return 2 with 7 -122 stored in var1  and  5  stored  in  var2.   Note  that  the
            integers  returned are signed, but they can be converted to unsigned 8-bit quantities
            using an expression like:
                   set num [expr { $num & 0xff }]

       s    The data is interpreted as count 16-bit signed integers represented in  little-endian
            byte  order.   The  integers  are stored in the corresponding variable as a list.  If
            count is *, then all of the remaining bytes in string will be scanned.  If  count  is
            omitted, then one 16-bit integer will be scanned.  For example,
                   binary scan \x05\x00\x07\x00\xf0\xff s2s* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.  Note that the integers
            returned are signed, but they can be converted to unsigned 16-bit quantities using an
            expression like:
                   set num [expr { $num & 0xffff }]

       S    This form is the same as s except that the data is interpreted as count 16-bit signed
            integers represented in big-endian byte order.  For example,
                   binary scan \x00\x05\x00\x07\xff\xf0 S2S* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.

       t    The data is interpreted as count 16-bit signed integers  represented  in  the  native
            byte order of the machine running the Tcl script.  It is otherwise identical to s and
            S.  To determine what the native byte order of the machine is, refer to the byteOrder
            element of the tcl_platform array.

       i    The  data is interpreted as count 32-bit signed integers represented in little-endian
            byte order.  The integers are stored in the corresponding variable  as  a  list.   If
            count  is  *, then all of the remaining bytes in string will be scanned.  If count is
            omitted, then one 32-bit integer will be scanned.  For example,
                   set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
                   binary scan $str i2i* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.  Note that the integers
            returned are signed, but they can be converted to unsigned 32-bit quantities using an
            expression like:
                   set num [expr { $num & 0xffffffff }]

       I    This form is the same as I except that the data is interpreted as count 32-bit signed
            integers represented in big-endian byte order.  For example,
                   set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
                   binary scan $str I2I* var1 var2
            will return 2 with 5 7 stored in var1 and -16 stored in var2.

       n    The  data  is  interpreted  as count 32-bit signed integers represented in the native
            byte order of the machine running the Tcl script.  It is otherwise identical to i and
            I.  To determine what the native byte order of the machine is, refer to the byteOrder
            element of the tcl_platform array.

       w    The data is interpreted as count 64-bit signed integers represented in  little-endian
            byte  order.   The  integers  are stored in the corresponding variable as a list.  If
            count is *, then all of the remaining bytes in string will be scanned.  If  count  is
            omitted, then one 64-bit integer will be scanned.  For example,
                   set str \x05\x00\x00\x00\x07\x00\x00\x00\xf0\xff\xff\xff
                   binary scan $str wi* var1 var2
            will  return 2 with 30064771077 stored in var1 and -16 stored in var2.  Note that the
            integers returned are signed and cannot be represented by Tcl as unsigned values.

       W    This form is the same as w except that the data is interpreted as count 64-bit signed
            integers represented in big-endian byte order.  For example,
                   set str \x00\x00\x00\x05\x00\x00\x00\x07\xff\xff\xff\xf0
                   binary scan $str WI* var1 var2
            will return 2 with 21474836487 stored in var1 and -16 stored in var2.

       m    The  data  is  interpreted  as count 64-bit signed integers represented in the native
            byte order of the machine running the Tcl script.  It is otherwise identical to w and
            W.  To determine what the native byte order of the machine is, refer to the byteOrder
            element of the tcl_platform array.

       f    The data is interpreted as count  single-precision  floating  point  numbers  in  the
            machine's  native  representation.   The  floating  point  numbers  are stored in the
            corresponding variable as a list.  If count is *, then all of the remaining bytes  in
            string  will  be  scanned.   If  count is omitted, then one single-precision floating
            point number will be scanned.  The size of a floating point number  may  vary  across
            architectures,  so  the  number of bytes that are scanned may vary.  If the data does
            not represent a valid floating point number, the resulting  value  is  undefined  and
            compiler  dependent.   For  example,  on a Windows system running on an Intel Pentium
            processor,
                   binary scan \x3f\xcc\xcc\xcd f var1
            will return 1 with 1.6000000238418579 stored in var1.

       r    This form is the same as f except that the  data  is  interpreted  as  count  single-
            precision  floating  point  number  in  little-endian  order.  This conversion is not
            portable to the minority of systems not using IEEE floating point representations.

       R    This form is the same as f except that the  data  is  interpreted  as  count  single-
            precision floating point number in big-endian order.  This conversion is not portable
            to the minority of systems not using IEEE floating point representations.

       d    This form is the same as f except that the  data  is  interpreted  as  count  double-
            precision floating point numbers in the machine's native representation. For example,
            on a Windows system running on an Intel Pentium processor,
                   binary scan \x9a\x99\x99\x99\x99\x99\xf9\x3f d var1
            will return 1 with 1.6000000000000001 stored in var1.

       q    This form is the same as d except that the  data  is  interpreted  as  count  double-
            precision  floating  point  number  in  little-endian  order.  This conversion is not
            portable to the minority of systems not using IEEE floating point representations.

       Q    This form is the same as d except that the  data  is  interpreted  as  count  double-
            precision floating point number in big-endian order.  This conversion is not portable
            to the minority of systems not using IEEE floating point representations.

       x    Moves the cursor forward count bytes in string.  If count is * or is larger than  the
            number  of  bytes  after  the  current cursor position, then the cursor is positioned
            after the last byte in string.  If count is omitted, then the cursor is moved forward
            one byte.  Note that this type does not consume an argument.  For example,
                   binary scan \x01\x02\x03\x04 x2H* var1
            will return 1 with 0304 stored in var1.

       X    Moves  the  cursor  back  count bytes in string.  If count is * or is larger than the
            current cursor position, then the cursor is positioned at location 0 so that the next
            byte  scanned  will be the first byte in string.  If count is omitted then the cursor
            is moved back one byte.  Note that this type  does  not  consume  an  argument.   For
            example,
                   binary scan \x01\x02\x03\x04 c2XH* var1 var2
            will return 2 with 1 2 stored in var1 and 020304 stored in var2.

       @    Moves  the  cursor  to  the  absolute location in the data string specified by count.
            Note that position 0 refers to the first byte  in  string.   If  count  refers  to  a
            position beyond the end of string, then the cursor is positioned after the last byte.
            If count is omitted, then an error will be generated.  For example,
                   binary scan \x01\x02\x03\x04 c2@1H* var1 var2
            will return 2 with 1 2 stored in var1 and 020304 stored in var2.

PORTABILITY ISSUES

       The r, R, q and Q conversions will  only  work  reliably  for  transferring  data  between
       computers  which  are all using IEEE floating point representations.  This is very common,
       but not universal.  To transfer floating-point numbers portably between all architectures,
       use their textual representation (as produced by format) instead.

EXAMPLES

       This  is  a  procedure  to  write  a  Tcl string to a binary-encoded channel as UTF-8 data
       preceded by a length word:

              proc writeString {channel string} {
                  set data [encoding convertto utf-8 $string]
                  puts -nonewline [binary format Ia* \
                          [string length $data] $data]
              }

       This procedure reads a string from a channel that was written by the previously  presented
       writeString procedure:

              proc readString {channel} {
                  if {![binary scan [read $channel 4] I length]} {
                      error "missing length"
                  }
                  set data [read $channel $length]
                  return [encoding convertfrom utf-8 $data]
              }

       This converts the contents of a file (named in the variable filename) to base64 and prints
       them:

              set f [open $filename rb]
              set data [read $f]
              close $f
              puts [binary encode base64 -maxlen 64 $data]

SEE ALSO

       encoding(3tcl), format(3tcl), scan(3tcl), string(3tcl), tcl_platform(3tcl)

KEYWORDS

       binary, format, scan