实战Tcl和TK程序设计 第一章 TCL基础

§0    序言

Tcl(Tool Command Language)包含脚本语言以及该脚本语言的解释器.该解释器可以很容易低地嵌入倒你的应用程序中.

       Tcl 的实质是工具之间的相互协作.

为什么要使用TCL?

       适合自动化处理

与TCL的C函数库用清晰的接口,并便于使用.Tcl和Tk提供了可移植的虚拟机

扩展性好,最著名的扩展是Tk. 它的优点,开发周期快,用户界面接口良好.

       与其他语言比,结构简单,类似C,可以通过编制C过程来增添新的Tcl原语,易学.

       其他:Tcl也支持Java和浏览器中运行.

TCL 相关网址:

      

 

 

§1    TCL的基本知识

本章描述TCL脚本语言的基本语法规则。包含了TCL解释器的基本机制：替换和分组。并涉及了以下命令：puts,
format, set, expr, string, while, incr, and proc.

TCL是基于命令的字符串语言，它的基本机制和字符串以及字符串替换有关。

TCL 命令

TCL命令处理器行为的三个基本步骤:

变元分组

对嵌套命令,变量和反斜杠换码序列进行替换

调用命令

 

Hello world 实例:

[root@Meil89 meil]# tclsh

% puts stdout {hello world!} 

hello world!

 

变量

Puts是命令, 后面的是变元

花括号内的整体是一个变元

 

变量

% set var 5

5

% set b $var

5

% puts $var

5

%

命令替换

嵌套命令由方括号来界定, 类似shell命令的逆向引号,还可以支持命令的任意嵌套.

% set len [string length foobar]  

6

 

数学表达式

Expr 专门执行运算,TCL 解释器不处理. 运算内容用花括号括起来,效率比较高点

% expr 7.2/4

1.8

 

设定精度:

expr 1 / 3

=> 0

expr 1 / 3.0

=> 0.333333333333

set tcl_precision 17

=> 17

expr 1 / 3.0

# The trailing 1 is the IEEE rounding digit

=> 0.33333333333333331

 

反斜杠替换

List可以代替大量的反斜杠

TCL只进行一遍解释, 不过eval不是

使用花括号和双引号进行分组

双引号会进行替换,花括号不会.在晚些时候替换一般使用花括号. 引号经常与format一起使用,puts默认已经有一个换行.

       分组在替换之前进行

过程

语法如下:

proc name arglist body

本书中过程名以大写字母开头,变量名以小写开头.

While 和if 后面的花括号一般要和条件在一行,不在一行要添加反斜杠.条件的判断一般要用花括号括起来.以延迟替换.

阶乘的实例:

% proc Factorial {x} {

   set i 1; set product 1

   while {$i <= $x} {

      set product [expr {$product * $i}]

      incr i

   }

   return $product

}

% Factorial 10

3628800

指针变量:

set var {the value of var}

=> the value of var

set name var

=> var

set name

=> var

set $name

=> the value of var

确定变量是否存在

if {![info exists foobar]} {

   set foobar 0

} else {

   incr foobar

}

注释

开头的#才是注释,其他的不是,这样实现:

# Here are some parameters

set rate 7.0    ;# The interest rate

set months 60   ;# The loan term

#注释中,反斜杠依然有效.,花括号也依然有用,所以注释中要小心这个两个符号

 

Reference

Backslash Sequences

Table 1-1. Backslash sequences
\a	Bell. (0x7)
\b	Backspace. (0x8)
\f	Form feed. (0xc)
\n	Newline. (0xa)
\r	Carriage return. (0xd)
\t	Tab. (0x9)
\v	Vertical tab. (0xb)
\	Replace the newline and the leading white space on the next line with a space.
\\	Backslash. ('\')
\ooo	Octal specification of character code. 1, 2, or 3 octal digits (0-7).
\xhh	Hexadecimal specification of character code. 1 or 2 hex digits. Be careful when using this in a string of characters, because all hexadecimal characters following the \x will be consumed, but only the last 2 will specify the value.
\uhhhh	Hexadecimal specification of a 16-bit Unicode character value. 4 hex digits.
\c	Replaced with literal c if c is not one of the cases listed above. In particular, \$, \", \{, \}, \], and \[ are used to obtain these characters.

Arithmetic Operators

Table 1-2. Arithmetic operators from highest to lowest precedence
- ~ !	Unary minus, bitwise NOT, logical NOT.
* / %	Multiply, divide, remainder.
+ -	Add, subtract.
<< >>	Left shift, right shift.
< > <= >=	Comparison: less, greater, less or equal, greater or equal.
== != eq ne	Equal, not equal, string equal (Tcl 8.4), string not equal (Tcl 8.4).
&	Bitwise AND.
^	Bitwise XOR.
|	Bitwise OR.
&&	Logical AND.
||	Logical OR.
x?y:z	If x then y else z.

Built-in Math Functions

Table 1-3. Built-in math functions
acos(x)	Arccosine of x.
asin(x)	Arcsine of x.
atan(x)	Arctangent of x.
atan2(y,x)	Rectangular (x,y) to polar (r,th). atan2 gives th.
ceil(x)	Least integral value greater than or equal to x.
cos(x)	Cosine of x.
cosh(x)	Hyperbolic cosine of x.
exp(x)	Exponential, ex.
floor(x)	Greatest integral value less than or equal to x.
fmod(x,y)	Floating point remainder of x/y.
hypot(x,y)	Returns sqrt(x*x + y*y). r part of polar coordinates.
log(x)	Natural log of x.
log10(x)	Log base 10 of x.
pow(x,y)	x to the y power, xy.
sin(x)	Sine of x.
sinh(x)	Hyperbolic sine of x.
sqrt(x)	Square root of x.
tan(x)	Tangent of x.
tanh(x)	Hyperbolic tangent of x.
abs(x)	Absolute value of x.
double(x)	Promote x to floating point.
int(x)	Truncate x to an integer.
round(x)	Round x to an integer.
rand()	Return a random floating point value between 0.0 and 1.0.
srand(x)	Set the seed for the random number generator to the integer x.
wide(x)	Promote x to a wide (64-bit) integer. (Tcl 8.4)

Core Tcl Commands

The pages listed in Table 1-4 give the primary references for the command.

Table 1-4. Built-in Tcl commands
Command	Pg.	Description
after	228	Schedule a Tcl command for later execution.
append	56	Append arguments to a variable's value. No spaces added.
array	97	Query array state and search through elements.
binary	59	Convert between strings and binary data.
break	83	Exit loop prematurely.
catch	83	Trap errors.
cd	122	Change working directory.
clock	183	Get the time and format date strings.
close	121	Close an open I/O stream.
concat	65	Concatenate arguments with spaces between. Splices lists.
console	29	Control the console used to enter commands interactively.
continue	83	Continue with next loop iteration.
error	85	Raise an error.
eof	116	Check for end of file.
eval	130	Concatenate arguments and evaluate them as a command.
exec	105	Fork and execute a UNIX program.
exit	124	Terminate the process.
expr	6	Evaluate a math expression.
fblocked	233	Poll an I/O channel to see if data is ready.
fconfigure	231	Set and query I/O channel properties.
fcopy	250	Copy from one I/O channel to another.
file	108	Query the file system.
fileevent	229	Register callback for event-driven I/O.
flush	116	Flush output from an I/O stream's internal buffers.
for	82	Loop construct similar to C for statement.
foreach	79	Loop construct over a list, or lists, of values.
format	56	Format a string similar to C sprintf.
gets	119	Read a line of input from an I/O stream.
glob	122	Expand a pattern to matching file names.
global	90	Declare global variables.
history	196	Use command-line history.
if	76	Test a condition. Allows else and elseif clauses.
incr	12	Increment a variable by an integer amount.
info	186	Query the state of the Tcl interpreter.
interp	292	Create additional Tcl interpreters.
join	72	Concatenate list elements with a given separator string.
lappend	66	Add elements to the end of a list.
lindex	68	Fetch an element of a list.
linsert	68	Insert elements into a list.
list	65	Create a list out of the arguments.
llength	68	Return the number of elements in a list.
load	697	Load shared libraries that define Tcl commands.
lrange	68	Return a range of list elements.
lreplace	68	Replace elements of a list.
lsearch	69	Search for an element of a list that matches a pattern.
lset	62	Set an element in a list. (Tcl 8.4)
lsort	70	Sort a list.
namespace	213	Create and manipulate namespaces.
open	116	Open a file or process pipeline for I/O.
package	175	Provide or require code packages.
pid	124	Return the process ID.
proc	87	Define a Tcl procedure.
puts	119	Output a string to an I/O stream.
pwd	122	Return the current working directory.
read	120	Read blocks of characters from an I/O stream.
regexp	158	Match regular expressions.
regsub	162	Substitute based on regular expressions.
rename	88	Change the name of a Tcl command.
return	86	Return a value from a procedure.
scan	58	Parse a string according to a format specification.
seek	121	Set the seek offset of an I/O stream.
set	5	Assign a value to a variable.
socket	239	Open a TCP/IP network connection.
source	26	Evaluate the Tcl commands in a file.
split	71	Chop a string up into list elements.
string	49	Operate on strings.
subst	140	Substitute embedded commands and variable references.
switch	77	Test several conditions.
tell	121	Return the current seek offset of an I/O stream.
time	202	Measure the execution time of a command.
trace	193	Monitor variable assignments.
unknown	178	Handle unknown commands.
unset	13	Delete variables.
uplevel	138	Execute a command in a different scope.
upvar	91	Reference a variable in a different scope.
variable	207	Declare namespace variables.
vwait	230	Wait for a variable to be modified.
while	79	Loop until a boolean expression is false.