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词条 TCL语言
释义

Tcl (最早称为“工具命令语言”"Tool Command Language", 但是目前已经不是这个含义,不过我们仍然称呼它为TCL)是一种 脚本语言。 由John Ousterhout创建。 TCL很好学,功能很强大。TCL经常被用于 快速原型开发,脚本编程, GUI和测试等方面。

基本概念

Tcl (最早称为“工具命令语言”"Tool Command Language", 但是目前已经不是这个含义,不过我们仍然称呼它为TCL)是一种 脚本语言。 由John Ousterhout创建。 TCL很好学,功能很强大。TCL经常被用于 快速原型开发,脚本编程, GUI和测试等方面。TCL念作“踢叩” "tickle". Tcl的特性包括:

* 任何东西都是一条命令,包括语法结构(for, if等)。

* 任何事物都可以重新定义和重载。

* 所有的数据类型都可以看作字符串。

* 语法规则相当简单

* 提供事件驱动给Socket和文件。基于时间或者用户定义的事件也可以。

* 动态的域定义。

* 很容易用C, C++,或者Java扩展。

* 解释语言,代码能够动态的改变。

* 完全的Unicode支持。

* 平台无关。Win32, UNIX, Mac 上都可以跑。

* 和Windows的GUI紧密集成。 Tk

* 代码紧凑,易于维护。

TCL本身不提供面向对象的支持。但是语言本身很容易扩展到支持面向对象。许多C语言扩展都提供面向对象能力,包括XOTcl, Incr Tcl 等。另外SNIT扩展本身就是用TCL写的。

使用最广泛的TCL扩展是TK。 TK提供了各种OS平台下的图形用户界面GUI。连强大的Python语言都不单独提供自己的GUI,而是提供接口适配到TK上。另一个流行的扩展包是Expect. Expect提供了通过终端自动执行命令的能力,例如(passwd, ftp, telnet等命令驱动的外壳).

具体例子

下面是TCL程序的例子:

#!/bin/sh

# next line restarts using tclsh in path \\

exec tclsh ${1+"$@"}

# echo server that can handle multiple

# simultaneous connections.

proc newConnection { sock addr port } {

# client connections will be handled in

# line-buffered, non-blocking mode

fconfigure $sock -blocking no -buffering line

# call handleData when socket is readable

fileevent $sock readable [ list handleData $sock ]

}

proc handleData {

puts $sock [ gets $sock ]

if { [ eof $sock ] } {

close $sock

}

}

# handle all connections to port given

# as argument when server was invoked

# by calling newConnection

set port [ lindex $argv 0 ]

socket -server newConnection $port

# enter the event loop by waiting

# on a dummy variable that is otherwise

# unused.

vwait forever

另外一个TK的例子 (来自 A simple A/D clock) 它使用了定时器时间,3行就显示了一个时钟。

proc every {ms body} {eval $body; after $ms [info level 0]}

pack [label .clock -textvar time]

every 1000 {set ::time [clock format [clock sec] -format %H:%M:%S]} ;# RS

解释:第一行定义了过程every, 每隔ms毫秒,就重新执行body代码。第二行创建了标签起内容由time变量决定。第3行中设置定时器,time变量从当前时间中每秒更新一次。

Tcl被广泛的用做script语言,大多数情况下,Tcl和Tk(“Tool Kit”)库同时使用,Tk是一系列令Tcl易于编写图形用户接口的命令和过程

Tcl的一个重要特性是它的扩展性。如果一个程序需要使用某些标准Tcl没有提供的功能,可以使用c语言创造一些新的Tcl命令,并很容易的融合进去。正是由于Tcl易于扩展,很多人为它编写了扩展包,并在网上共享。

Tcl和其他编程语言例如c不同,它是一种解释语言而非编译语言。Tcl程序由一系列Tcl命令组成,在运行时由Tcl解释器解释运行。解释运行的一个优点是它可以自己为自己生成Tcl script。

变量和变量交换

不像c,Tcl的变量在使用前不需要声明。Tcl的变量在它首次被赋值时产生,使用set命令。变量可以用unset命令删除,虽然并不强制需要这样做。

变量的值通过$符号访问,也叫变量交换。

Tcl是一个典型的”弱类型定义”语言,这意味者任何类型可以存储在任何变量中。例如,同一个变量可以存储数字,日期,字符串甚至另一段Tcl script.

Example 1.1:

set foo "john"

puts "Hi my name is $foo"

Output: Hi my name is john

Example 1.2:

set month 2

set day 3

set year 97

set date "$month:$day:$year"

puts $date

Output: 2:3:97

Example 1.3:

set foo "puts hi"

eval $foo

Output: hi

在这个例子里,变量foo存储了另外一段Tcl script.

表达式

包括数学表达式,关系表达式,通常用 expr命令。

Example 2.1:

expr 0 == 1

Output: 0

Example 2.2:

expr 1 == 1

Output: 1

两数比较,true则输出1,false输出0

Example 2.3:

expr 4 + 5

Output: 9

Example 2.4:

expr sin(2)

Output: 0.909297

命令传递

以运算结果替代Tcl命令中的部分

Example 3.1:

puts "I am [expr 10 * 2] years old, and my I.Q. is [expr 100 - 25]"

Output: I am 20 years old, and my I.Q. is 75

方括号是命令传递的标志

Example 3.2:

set my_height 6.0

puts "If I was 2 inches taller, I would be [expr $my_height + (2.0 / 12.0)] feet tall"

Output: If I was 2 inches taller, I would be 6.16667 feet tall

命令流控制

Tcl有判断流转(if-else; switch)和循环控制(while; for; foreach)

Example 4.1:

set my_planet "earth"

if {$my_planet == "earth"} {

puts "I feel right at home."

} elseif {$my_planet == "venus"} {

puts "This is not my home."

} else {

puts "I am neither from Earth, nor from Venus."

}

set temp 95

if {$temp < 80} {

puts "It's a little chilly."

} else {

puts "Warm enough for me."

}

Output:

I feel right at home.

Warm enough for me.

Example 4.2:

set num_legs 4

switch $num_legs {

2 {puts "It could be a human."}

4 {puts "It could be a cow."}

6 {puts "It could be an ant."}

8 {puts "It could be a spider."}

default {puts "It could be anything."}

}

Output:

It could be a cow.

Example 4.3:

for {set i 0} {$i < 10} {incr i 1} {

puts "In the for loop, and i == $i"

}

Output:

In the for loop, and i == 0

In the for loop, and i == 1

In the for loop, and i == 2

In the for loop, and i == 3

In the for loop, and i == 4

In the for loop, and i == 5

In the for loop, and i == 6

In the for loop, and i == 7

In the for loop, and i == 8

In the for loop, and i == 9

Example 4.4:

set i 0

while {$i < 10} {

puts "In the while loop, and i == $i"

incr i 1

}

Output:

In the while loop, and i == 0

In the while loop, and i == 1

In the while loop, and i == 2

In the while loop, and i == 3

In the while loop, and i == 4

In the while loop, and i == 5

In the while loop, and i == 6

In the while loop, and i == 7

In the while loop, and i == 8

In the while loop, and i == 9

Example 4.5:

foreach vowel {a e i o u} {

puts "$vowel is a vowel"

}

Output:

a is a vowel

e is a vowel

i is a vowel

o is a vowel

u is a vowel

Procedures

参数定义方法

Tcl的Procedures 和c的函数差不多. 它们有参数,它们返回值。基本定义方法是:

proc name argList body

当一个procedure被定义,它就被看做是一个命令,如同Tcl的自带命令一样,通过名字来呼叫,名字后面跟上参数。

缺省的,procedure的返回值是它的最后一个命令结果。但也可以通过return命令来返回其他值。Return值可以在procedure的任何地方,一旦执行,procedure就此返回。

Example 5.1:

proc sum_proc {a b} {

return [expr $a + $b]

}

proc magnitude {num} {

if {$num > 0} {

return $num

}

set num [expr $num * (-1)]

return $num

}

set num1 12

set num2 14

set sum [sum_proc $num1 $num2]

puts "The sum is $sum"

puts "The magnitude of 3 is [magnitude 3]"

puts "The magnitude of -2 is [magnitude -2]"

Output:

The sum is 26

The magnitude of 3 is 3

The magnitude of -2 is 2

在procedure中可以通过set创造变量,但是变量只在procedure中有效,而且一旦procedure返回,这些变量就不可访问。如果procedure需要访问主程序中的变量,就需要使用global关键字。

Example 5.2:

proc dumb_proc {} {

set myvar 4

puts "The value of the local variable is $myvar"

global myglobalvar

puts "The value of the global variable is $myglobalvar"

}

set myglobalvar 79

dumb_proc

Output:

The value of the local variable is 4

The value of the global variable is 79

List

Lists就好像是Tcl中的一种特殊的数组。它把一堆东西放成一个集合,然后就像操作一个整体一样的操作它。

Example 6.1:

set simple_list "John Joe Mary Susan"

puts [lindex $simple_list 0]

puts [lindex $simple_list 2]

Output:

John

Mary

注意list的index是从0开始的

Example 6.2:

set simple_list2 "Mike Sam Heather Jennifer"

set compound_list [list $simple_list $simple_list2]

puts $compound_list

puts [llength $compound_list]

Output:

{John Joe Mary Susan} {Mike Sam Heather Jennifer}

2

Example 6.3:

set mylist "Mercury Venus Mars"

puts $mylist

set mylist [linsert $mylist 2 Earth]

puts $mylist

lappend mylist Jupiter

puts $mylist

Output:

Mercury Venus Mars

Mercury Venus Earth Mars

Mercury Venus Earth Mars Jupiter

Arrays

Tcl数组在使用前无须定义,大小也不用指定。

Example 7.1:

set myarray(0) "Zero"

set myarray(1) "One"

set myarray(2) "Two"

for {set i 0} {$i < 3} {incr i 1} {

puts $myarray($i)

}

Output:

Zero

One

Two

Example 7.2:

set person_info(name) "Fred Smith"

set person_info(age) "25"

set person_info(occupation) "Plumber"

foreach thing {name age occupation} {

puts "$thing == $person_info($thing)"

}

Output:

name == Fred Smith

age == 25

occupation == Plumber

这个例子指出数组的index不需要是数字,其他类型的数据也可以。

Example 7.3:

set person_info(name) "Fred Smith"

set person_info(age) "25"

set person_info(occupation) "Plumber"

foreach thing [array names person_info] {

puts "$thing == $person_info($thing)"

}

Output:

occupation == Plumber

age == 25

name == Fred Smith

Strings

字符串是Tcl中最常用的类型,string有很多使用参数,可以参照Tcl手册。使用方法:

string option arg arg ...

Example 8.1:

set str "This is a string"

puts "The string is: $str"

puts "The length of the string is: [string length $str]"

puts "The character at index 3 is: [string index $str 3]"

puts "The characters from index 4 through 8 are: [string range $str 4 8]"

puts "The index of the first occurrence of letter \\"i\\" is: [string first i $str]"

Output:

The string is: This is a string

The length of the string is: 16

The character at index 3 is: s

The characters from index 4 through 8 are: is a

The index of the first occurrence of letter "i" is: 2

Input/Output

Tcl的绝大多数输入/输出是通过puts和gets做到的。Puts命令显示在console上,gets命令从console输入上取得数据,并存储在某个变量中。

gets channelId varName

channelID可以理解为c的文件句柄,varName如果定义,输入值就赋给它,gets返回读入的字节数,否则gets直接返回输入值。

Example 9.1:

puts -nonewline "Enter your name: "

set bytesread [gets stdin name]

puts "Your name is $name, and it is $bytesread bytes long"

Output: (note that user input is shown in italics)

Enter your name: Shyam

Your name is Shyam, and it is 5 bytes long

Example 9.2:

set f [open "/tmp/myfile" "w"]

puts $f "We live in Texas. It's already 110 degrees out here."

puts $f "456"

close $f

Output: (none)

Open打开了一个 "/tmp/myfile" 作为channel. 用法是:

open name access

access参数指出打开文件的方式,”w”是读写。这时可以用puts $f把内容写入文件

Example 9.3:

set f [open "/tmp/myfile" "r"]

set line1 [gets $f]

set len_line2 [gets $f line2]

close $f

puts "line 1: $line1"

puts "line 2: $line2"

puts "Length of line 2: $len_line2"

Output:

line 1: We live in Texas. It's already 110 degrees out here.

line 2: 456

Length of line 2: 3

这个例子假设已知文件只有两行,如果不是,则需要使用循环,用eof来找到文件尾。

eval

eval命令会把它的参数直接送往解释器。

Example 10.1:

set foo "set a 22"

eval $foo

puts $a

Output:

22

单纯的执行$foo不会成功。

catch

Example 10.2:

set retval [catch {set f [open "nosuchfile" "r"]}]

if {$retval == 1} {

puts "An error occured"

}

Output: (this output occurs if there is no file named "nosuchfile" in the current directory).

An error occured

Catch 参数记录一个script的执行情况,如果返回值为1,则执行出错。用来进行错误处理。

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