binary - Insert and extract fields from binary strings
binary decode format ?-option value ...? data | binary encode format ?-option value ...? data | binary format formatString ?arg arg ...? binary scan string formatString ?varName varName ...?
binary(1t) Tcl Built-In Commands binary(1t)
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NAME
binary - Insert and extract fields from binary strings
SYNOPSIS
binary decode format ?-option value ...? data |
binary encode format ?-option value ...? data |
binary format formatString ?arg arg ...?
binary scan string formatString ?varName varName ...?
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DESCRIPTION
This command provides facilities for manipulating binary data. The
subcommand binary format creates a binary string from normal Tcl val-
ues. For example, given the values 16 and 22, on a 32-bit architec-
ture, 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 hexadec- |
imal 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 addi-
tional arguments. The resulting binary value is returned.
The formatString consists of a sequence of zero or more field speci-
fiers separated by zero or more spaces. Each field specifier is a sin-
gle 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 spec-
ifiers 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 speci-
fier. 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 char-
acter is used, and the high byte discarded) so when storing char-
acter 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 trun-
cation 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 for-
matted. If count is omitted, then one character will be format-
ted. 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 truncat-
ing 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 dig-
its. If arg has more than the specified number of digits, the
extra digits will be ignored. If count is *, then all of the dig-
its 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 ele-
ments 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 run-
ning. 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 run-
ning. 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 over-
flows 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-preci-
sion. For example, on a Windows system running on an Intel Pen-
tium 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 represen-
tation (very common, but not universal.)
R This form is the same as r except that it stores the single-preci-
sion 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 lit-
tle-endian order. This conversion only produces meaningful output
when used on machines which use the IEEE floating point represen-
tation (very common, but not universal.)
Q This form is the same as q except that it stores the double-preci-
sion 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 cur-
sor 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 gener-
ated. 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 vari-
able.
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 char-
acter followed by an optional numeric count. Most field specifiers
consume one argument to obtain the variable into which the scanned val-
ues 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 cur-
rent 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 sub-
command:
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 sys-
tems) will be scanned into long data size values. In doing this, val-
ues 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 vari-
able. 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 omit-
ted, 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 con-
verted 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 repre-
sented 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 omit-
ted, 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 con-
verted 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 repre-
sented 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 repre-
sented 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 omit-
ted, 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 con-
verted 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 repre-
sented 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 repre-
sented 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 omit-
ted, 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 repre-
sented 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 depen-
dent. For example, on a Windows system running on an Intel Pen-
tium 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 posi-
tion, 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 posi-
tioned 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 spec-
ified 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 repre-
sentations. 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]
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/tcl-8 |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
encoding(n), format(n), scan(n), string(n), tcl_platform(n)
KEYWORDS
binary, format, scan
NOTES
Source code for open source software components in Oracle Solaris can
be found at https://www.oracle.com/downloads/opensource/solaris-source-
code-downloads.html.
This software was built from source available at
https://github.com/oracle/solaris-userland. The original community
source was downloaded from http://prdownloads.sourceforge.net/tcl/tcl-
core8.6.7-src.tar.gz.
Further information about this software can be found on the open source
community website at https://www.tcl.tk/.
Tcl 8.0 binary(1t)