Programming Using Tcl/Tk

1. Programming Using Tcl/Tk These slides are based upon several Tcl/Tk text books material byDr. Ernest J. Friedman-Hill

2. What you’ll need • PCs in the Computer Science Lab have it installed • Start / Tcl / Wish • Start / Widget tour • Or install it on your own computer • Windows & Macintosh: free binaries available • Most Unix: source available • Documentation • books can be bought (bookstore, etc) • books in the PC lab • up-to-date man pages on-line • Start / Help

3. What is Tcl/Tk? • Tcl • a scripting language • can be extended in C (but this is harder) • ugly but simple • Tk • a simple but powerful widget set • Hello World: a complete program that exits when a person presses the button • grid [ button .myButton -text "Hello World" -command exit ] • Simple things are simple, hard things are possible

4. Tcl Language Programming There are two parts to learning Tcl: 1. Syntax and substitution rules: • Substitutions simple (?), but may be confusing at first. 2. Built-in commands: • Can learn individually as needed. • Control structures are commands, not language syntax.

5. Scripts and Commands • Tcl script = • Sequence of commands. • Commands separated by newlines, semi-colons. • Tcl command = • One or more words separated by white space. • First word is command name, others are arguments. • Returns string result. • Examples: set myName Saul puts "My Name is $myName” set class CPSC-481; puts -nonewline $class

6. Arguments • Parser assigns no meaning to arguments (quoting by default, evaluation is special): set x 4 x is "4 " set y x+10 y is "x+10” set z $x+10 z is "4+10” • Different commands assign different meanings to their arguments. “Type-checking” must be done by commands themselves. expr 24/3 arg is math expresson -> 8 eval "set a 122" evaluate argument as a command button .b -text Hello -fg red some args are options (the -) string length Abracadabra some args are qualifiers (length)

7. Variable Substitution • Syntax: $varName • Variable name is letters, digits, underscores. • This is a little white lie, actually. • May occur anywhere in a word. Sample commandResult set b 66 66 set a b b set a $b 66 set a $b+$b+$b 66+66+66 set a $b.3 66.3 set a $b4no such variable

8. Command Substitution • Syntax: [script] • Evaluate script, substitute result. • May occur anywhere within a word. Sample commandResult set b 8 8 set a [expr $b+2] 10 set a "b-3 is [expr $b-3]" b-3 is 5

9. Controlling Word Structure • Words break at white space and semi-colons, except: • Double-quotes prevent breaks: set a 4; set y 5 set a "x is $x; y is $y" -> x is 4; y is 5 • Curly braces prevent breaks and substitutions: set a {[expr $b*$c]} ->[expr $b*$c] • Backslashes quote special characters: set a word\ with\ \$\ and\ space ->word with $ and space

10. Controlling Word Structure (continued) • Backslashes can escape newline (continuation) • set aLongVariableNameIsUnusual \“This is a string”-> This is a string • Substitutions don't change word structure: • set a "two words" set b $a-> two words

11. Comments • The # is the comment command • Tcl parsing rules apply to comments as well set a 22; set b 33 <- OK # this is a comment <- OK set a 22 # same thing? <- Wrong! set a 22 ;# same thing <- OK

12. Summary of Tcl Command Syntax • Command: words separated by whitespace • First word is a function, others are arguments • Only functions apply meanings to arguments • Single-pass tokenizing and substitution • $ causes variable interpolation • [ ] causes command interpolation • “” prevents word breaks • { } prevents all interpolation • \ escapes special characters • TCL HAS NO GRAMMAR!

13. Tcl Expressions • Arguments are interpretted as expressions in some commands: expr, if, ... Sample commandResult set b 5 5 expr ($b*4) - 3 17 expr $b <= 2 0 expr {$b * cos(4)} -3.268… • Some Tcl operators work on strings too(but safer to use the string compare command) set a Bill Bill expr {$a < "Anne"} 0 expr {$a < "Fred"} 1

14. Tcl Arrays • Tcl arrays are 'associative arrays': index is any string • set foo(fred) 44 ;# 44 • set foo(2) [expr $foo(fred) + 6] ;# 50 • array names foo ;# fred 2 • You can 'fake' 2-D arrays: set A(1,1) 10 set A(1,2) 11 array names A => 1,1 1,2 (commas included in names!)

15. Lists • Zero or more elements separated by white space: set colors {red green blue} • Braces and backslashes for grouping: set hierarchy {a b {c d e} f}) set two_item_list {one two\ two} • List-related commands: concat lindex llength lsearch foreach linsert lrange lsort lappend list lreplace • Note: all indices start with 0. end means last element • Examples: lindex {a b {c d e} f} 2 íc d e lsort {red green blue} íblue green red

16. String Manipulation • String manipulation commands: regexp format split string regsub scan join • string subcommands compare first last index length match range toupper tolower trim trimleft trimright • Note: all indexes start with 0. end means last char • string tolower "THIS" ;# this • string trimleft “XXXXHello” ;# Hello • string index “abcde” 2 ;# c

17. Control Structures • C-like in appearance. • Just commands that take Tcl scripts as arguments. • Commands: if for switch break foreach while eval continue

18. if else set x 2 if {$x < 3} { puts "x is less than 3" } else { puts "x is 3 or more" }

19. while #list reversal set a {a b c d e} set b "” set i [expr [llength $a] - 1] while {$i >= 0} { lappend b [lindex $a $i] incr i -1 } puts $b

20. for and foreach for {set i 0} {$i<10} {incr i} { puts $I } foreach color {red green blue} { puts “I like $color” } set A(1) a; set A(2) b; set A(26) z foreach index [array names A] { puts $A($index) }

21. switch set pete_count 0 set bob_count 0 set other_count 0 foreach name {Peter Peteee Bobus Me Bobor Bob} { switch -regexp $name { ^Pete* {incr pete_count} ^Bob|^Robert {incr bob_count} default {incr other_count} } } puts "$pete_count $bob_count $other_count"

22. Procedures • proc command defines a procedure: proc decrement {x} { expr $x-1 } • Procedures behave just like built-in commands: decrement 3 í2 • Arguments can have default values: proc decrement {x {y 1}} { expr $x-$y } decrement 100 5 ;# 95 decrement 100 ;# 99 name body list of argument names

23. Procedures • Procedures can have a variable number of arguments proc sum args { set s 0 foreach i $args { incr s $i } return $s} sum 1 2 3 4 5 í15 sum í0

24. Procedures and Scope • Scoping: local and global variables. • Interpreter knows variables by their name and scope • Each procedure introduces a new scope • global procedure makes a global variable local set outside "I'm outside" set inside "I'm really outside" proc whereAmI {inside} { global outside puts $outside puts $inside } whereAmI "I wonder where I will be" -> I'm outsideI wonder where I will be

25. Tcl File I/O • Tcl file I/O commands: open gets seek flush globclose read tell cd fconfigure fblocked fileeventputs source eof pwd filename • File commands use 'tokens' to refer to files set f [open "myfile.txt" "r"] => file4 puts $f "Write this text into file" close $f

26. Tcl File I/O • gets and puts are line oriented set x [gets $f] reads one line of $f into x • read can read specific numbers of bytes read $f 100 => (up to 100 bytes of file $f) • seek, tell, and read can do random-access I/O set f [open "database" "r"] seek $f 1024 read $f 100 => (bytes 1024-1123 of file $f)

27. Tcl Network I/O • socket creates a network connection set f [socket www.sun.com 80] fconfigure $f -buffering line puts $f "GET /" puts [read $f 100]close $f => The 1st 100 characters from Sun's home page • Network looks just like a file! • To create a server socket, just use socket -server accept portno