Programming Using Tcl/Tk Week 2 Seree Chinodom

What We'll Do Today u Tell me about yourselves u Review Tcl syntax from last week u Expressions u Lists u Strings and pattern matching u Control structures u Procedures u Error handling u File and network I/O and process management u Getting info at runtime

Who you are u Write on a piece of paper: –Your name –What you do –What you want to do with Tcl/Tk –Primary platform you use (UNIX, Wintel, Mac?) –What other computer languages you know –Anything you’d especially like to see covered

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

More On Substitutions  Keep substitutions simple: use commands like format for complex arguments.  Use eval for another level of expansion: exec rm *.o ํ *.o: No such file or directory glob *.o ํ a.o b.o exec rm [glob *.o] ํ a.o b.o: No such file or directory eval exec rm [glob *.o]

Tcl Expressions u C-like (int and double) u Command, variable substitution occurs within expressions.  Used in expr, if, other commands. Sample commandResult set b 55 expr ($b*4) expr $b <= 20 expr $a * cos(2*$b) expr {$b * [fac 4]}120 u Tcl will promote integers to reals when needed u All values translated to the same type  Note that expr knows about types, not Tcl!

Tcl Arrays u Tcl arrays are 'associative arrays': index is any string set x(fred) 44 set x(2) [expr $x(fred) + 6] array names x => fred 2 u 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!)

Tcl Expressions u What’s happening in these expressions? expr $a * cos(2*$b) $a, $b substituted by scanner before expr is called expr {$b * [fac 4]}120 here, $b is substituted by expr itself u Therefore, expressions get substituted more than once! set b \$a set a 4 expr $b * 28

Tcl String Expressions u Some Tcl operators work on strings too set a BillBill expr {$a < "Anne"}0 u, =, ==, and != work on strings u Beware when strings can look like numbers  You can also use the string compare function

Lists u Zero or more elements separated by white space: red green blue u Braces and backslashes for grouping: a b {c d e} f (4 words) one\ word two three (3 words) u List-related commands: concatlindexllengthlsearch foreachlinsertlrangelsort lappendlistlreplace  Note: all indices start with 0. end means last element u Examples: lindex {a b {c d e} f} 2 ํ c d e lsort {red green blue} ํ blue green red

Lists are Powerful u A list makes a handy stack Sample commandResult set stack 11 push stack redred 1 push stack {a fish}{a fish} red 1 pop stacka fish (stack is now red 1)  push and pop are very short and use list commands to do their work

More about Lists u A true list’s meaning won’t change when (re)scanned red $animal blue $animal <= not a list red fish blue fish <= list red \$fish blue \$fish <= not a list, but list red \$fish blue \$fish gives you… red {$fish} blue {$fish} <= which is a list u Commands and lists are closely related –A command is a list –Use eval to evaluate a list as a command

Commands And Lists: Quoting Hell u Lists parse cleanly as commands: each element becomes one word. u To create commands safely, use list commands: button.b -text Reset -command {set x $initValue} ( initValue read when button invoked)... -command "set x $initValue" (fails if initValue is " New York ": command is " set x New York ")... -command "set x {$initValue}" (fails if initValue is " { ": command is " set x {{} ")... -command [list set x $initValue] (always works: if initValue is " { " command is " set x \{ ") u List commands do all the work for you!

String Manipulation u String manipulation commands: regexpformatsplitstring regsubscanjoin  string subcommands compare first last index length match range toupper tolower trim trimleft trimright  Note: all indexes start with 0. end means last char

Globbing & Regular Expressions u "Globbing" - a simple pattern language –* means any sequence of characters –? matches any one character –[chars] matches and one character in chars –\c matches c, even if c is *, [, ?, etc. u Good for filename matching –*.exe, [A-E]*.txt, \?*.bak  glob command applies a glob pattern to filenames foreach f [glob *.exe] { puts "$f is a program" }

Globbing & Regular Expressions u "Regular Expressions" are a powerful pattern language –. (period) matches any character –^ matches start of a string –$ matches end of a string –\x single character escape –[chars] matches any of chars. ^: not. -: range. –(regexp) matches the regexp –* matches 0 or more of the preceding –+ matches 1 or more of the preceding –? matches 0 or 1 or the preceding –| can be used to divide alternatives.

Globbing & Regular Expressions u Examples: [A-Za-z0-9_]+ : valid Tcl identifiers T(cl|k) : Tcl or Tk  regexp command regexp T(cl|k) "I mention Tk" w t => returns 1 (match), w becomes "Tk", t gets "k" u regsub command regsub -nocase perl "I love Perl" Tcl mantra => returns 1 (match), mantra gets "I love Tcl" regsub -nocase {Where's ([a-z]*)\?} \ "Where's Bob?"{Who's \1?} result => returns 1 (match), result gets "Who's Bob?"

The format and scan Commands  format does string formatting. format "I know %d Tcl commands" 97 => I know 97 Tcl commands –has most of printf's capabilities –can also be use to create complex command strings  scan is like scanf set x "SSN#: # " scan $x "SSN#: %d" ssn puts "The social security number is $ssn" => The social security number is

Control Structures u C-like in appearance. u Just commands that take Tcl scripts as arguments. u Example: list reversal. Set list b to reverse of list a: set b "" set i [expr [llength $a] - 1] while {$i >= 0} { lappend b [lindex $a $i] incr i -1 } u Commands: ifforswitchbreak foreachwhileevalcontinue source

Control Structure Examples u if expr script u for script expr script script for {set i 0} {$i<10} {incr i} {... u switch (opt) string {p1 s1 p2 s2...} foreach name $my_name_list { switch -regexp $name { ^Pete* {incr pete_count} ^Bob|^Robert {incr bob_count} default {incr other_count} }

More on Control Structures u Brackets are never required - so watch out! set x 3 if $x>2 {... <= this is OK, eval’ed once while $x>2 {... <= this is NOT OK, eval’ed many times! set a {red blue green} foreach i $a <= this is OK foreach I red blue green {... NOT OK!  foreach [array names A] is a common idiom

Procedures  proc command defines a procedure: proc sub1 x {expr $x-1} u Procedures behave just like built-in commands: sub1 3 ํ 2 u Arguments can have default values: proc decr {x {y 1}} { expr $x-$y } name list of argument names body

Procedures and Scope u 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 x 10 > proc deltax {d} { set x [expr $x-$d] } > deltax 1 => can't read x: no such variable > proc deltax {d} { global x set x [expr $x-$d] } > deltax 1 => 9

Procedures and Scope  Note that global is an ordinary command proc tricky {varname} { global $varname set $varname "passing by reference"  upvar and uplevel let you do more complex things u level naming: (NOTE: Book is wrong (p. 84)) –#num : #0 is global, #1 is one call deep, #2 is 2… –num : 0 is current, 1 is caller, 2 is caller's caller… proc incr {varname} { upvar 1 $varname var set var [expr $var+1] }

Procedures and Scope  uplevel does for code what upvar does for variables proc loop {from to script} { set i $from while {$i <= $to} { uplevel $script incr i } set s "" loop 1 5 {set s $s*} puts $s => *****

More about Procedures u Variable-length argument lists: proc sum args { set s 0 foreach i $args { incr s $i } return $s } sum ํ 15 sum ํ 0

Errors u Errors normally abort commands in progress, application displays error message: set n 0 foreach i { } { set n [expr {$n + i*i}] } ํ syntax error in expression "$n + i*i"  Global variable errorInfo provides stack trace: set errorInfo ํ syntax error in expression "$n + i*i" while executing "expr {$n + i*i}" invoked from within "set n [expr {$n + i*i}]..." ("foreach" body line 2)...

Advanced Error Handling  Global variable errorCode holds machine-readable information about errors (e.g. UNIX errno value). NONE (in this case) u Can intercept errors (like exception handling): catch {expr {2 +}} msg ํ 1 (catch returns 0=OK, 1=err, other values...) set msg ํ syntax error in expression "2 +" u You can generate errors yourself (style question:) error "bad argument" return -code error "bad argument"

Tcl File I/O u Tcl file I/O commands: opengetsseekflushglob closereadtellcd fconfigure fblocked fileevent putssourceeofpwdfilename u File commands use 'tokens' to refer to files set f [open "myfile.txt" "r"] => file4 puts $f "Write this text into file" close $f

Tcl File I/O u 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 of file $f)

Tcl File I/O  fileevent lets you watch a file set f [open log r] fileevent $f readable \ {set data [read $f]; puts $f} u Doesn't seem to work right on Windows NT, others?  fblocked, fconfigure give you control over files fconfigure -buffering [line|full] fconfigure -blocking [true|false] fconfigure -translation [auto|binary|cr|lf|crlf] fblocked returns boolean

TCP, Ports, and Sockets u Networking uses layers of abstractions –In reality, there is current on a wire... u The Internet uses the TCP/IP protocol u Abstractions: –IP Addresses ( ) –Port numbers (80 for WWW, 25 for SMTP) u Sockets are built on top of TCP/IP u Abstraction: –Listening on a port for connections –Contacting a port on some machine for service u Tcl provides a simplified Socket library

Tcl Network I/O  socket creates a network connection set f [socket 80] fconfigure $f -buffering line puts $f "GET /" puts [read $f] => loads of HTML from Sun's home page u Network looks just like a file! u To create a server socket, just use socket -server accept portno

I/O and Processes  exec starts processes, and can use '&' set FAVORITE_EDITOR emacs exec $FAVORITE_EDITOR &  no filename expansion; use glob instead eval exec "ls [glob *.c]"  you can open pipes using open set f [open "|grep foo bar.tcl" "r"] while {[eof $f] != 0} { puts [gets $f] }

Runtime Information Facilities u Command line arguments –argc is count, argv0 is interp name, argv is list of args u Tcl/Tk version –tcl_version, tk_version (7.5, 4.1) u Platform-specific information –tk_platform array –osVersion, machine, platform, os –3.51, intel, windows, Windows NT on my box

Runtime Information Facilities  The info command what variables are there? –info vars, info globals, info locals, info exists what procedures have I defined, and how? –info procs, info args, info default, info body, info commands  the rename command –can rename any command, even built-in –can therfore replace any built-in command

Some More Interesting Tcl Features u Autoloading: – unknown invoked when command doesn't exist. –Loads Tcl procedures on demand from libraries. –Uses search path of directories.  load Tcl command –Long awaited standard interface for dynamic loading of Tcl commands from DLLs,.so's, etc.  interp Tcl command –You can create multiple independent Tcl interpreters in one process –interp -safe creates Safe-Tcl (sandbox) interpreters

Tcl 7.6 and Tk 4.2 u Major revision of grid geometry manager, needed for SpecTcl code generator (GUI builder)  C API change for channel (I/O) drivers (eliminate Tcl_File usage). u No other changes except bug fixes. u Now in beta release; final release in late September.

For Next Week... u Programming assignment #1: –Write a program which accepts, from a file or the keyboard, a list of programmers and the programming languages they know…: Barbara Modern: C++, Java, Eiffel Sam Slowpoke: FORTRAN IV, JPL –… and produces a report of languages and their users: C++: Barbara Modern, Tom Teriffic FORTRAN IV: Sam Slowpoke –Be sure to use procedures to modularize your program, and don't hard-code the names of any languages!

For Next Week... u Programming assignment #1 u Try to check out the Netscape Plug-in  Buy the reader and find pages about commands introduced since Ousterhout was published: fileevent, socket, fconfigure, interp, others... u Read Chapters 6 through 13 and 15 of Ousterhout