Programming Using TclTk Week 2

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Programming Using Tcl/TkWeek 2

• Dr. Ernest J. Friedman-Hill
• ejfried_at_herzberg.ca.sandia.gov
• http//herzberg.ca.sandia.gov/

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What We'll Do Today

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

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Who you are

• 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 youd especially like to see covered

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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!

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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

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Tcl Expressions

• C-like (int and double)
• Command, variable substitution occurs within
  expressions.
• Used in expr, if, other commands.
• Sample command Result
• set b 5 5
• expr (b4) - 3 17
• expr b lt 2 0
• expr a cos(2b) -5.03443
• expr b fac 4 120
• Tcl will promote integers to reals when needed
• All values translated to the same type
• Note that expr knows about types, not Tcl!

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Tcl Arrays

• Tcl arrays are 'associative arrays' index is any
  string
• set x(fred) 44
• set x(2) expr x(fred) 6
• array names x
• gt fred 2
• You can 'fake' 2-D arrays
• set A(1,1) 10
• set A(1,2) 11
• array names A
• gt 1,1 1,2 (commas included in names!)

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Tcl Expressions

• Whats happening in these expressions?
• expr a cos(2b) -5.03443
• a, b substituted by scanner before expr is
  called
• expr b fac 4 120
• here, b is substituted by expr itself
• Therefore, expressions get substituted more than
  once!
• set b \a
• set a 4
• expr b 2 8

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Tcl String Expressions

• Some Tcl operators work on strings too
• set a Bill Bill
• expr a lt "Anne" 0
• lt, gt, lt, gt, , and ! work on strings
• Beware when strings can look like numbers
• You can also use the string compare function

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Lists

• Zero or more elements separated by white space
• red green blue
• Braces and backslashes for grouping
• a b c d e f (4 words)
• one\ word two three (3 words)
• 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 ? c d e
• lsort red green blue ? blue green red

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Lists are Powerful

• A list makes a handy stack
• Sample command Result
• set stack 1 1
• push stack red red 1
• push stack a fish a fish red 1
• pop stack a fish
• (stack is now red 1)
• push and pop are very short and use list commands
  to do their work

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More about Lists

• A true lists meaning wont change when
  (re)scanned
• red animal blue animal lt not a listred fish
  blue fish lt list
• red \fish blue \fish lt not a list, but
• list red \fish blue \fish gives you
• red fish blue fish lt which is a list
• Commands and lists are closely related
• A command is a list
• Use eval to evaluate a list as a command

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Commands And Lists Quoting Hell

• Lists parse cleanly as commands each element
  becomesone word.
• 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 \")
• List commands do all the work for you!

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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

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Globbing Regular Expressions

• "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.
• 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"

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Globbing Regular Expressions

• "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.

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Globbing Regular Expressions

• Examples
• A-Za-z0-9_ valid Tcl identifiers
• T(clk) Tcl or Tk
• regexp command
• regexp T(clk) "I mention Tk" w t
• gt returns 1 (match), w becomes "Tk", t gets "k"
• regsub command
• regsub -nocase perl "I love Perl" Tcl mantra
• gt returns 1 (match), mantra gets "I love Tcl"
• regsub -nocase Where's (a-z)\? \
• "Where's Bob? Who's \1? result
• gt returns 1 (match), result gets "Who's Bob?"

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The format and scan Commands

• format does string formatting.
• format "I know d Tcl commands" 97
• gt 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 148766207"
• scan x "SSN d" ssn
• puts "The social security number is ssn"
• gt The social security number is 148766207

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Control Structures

• C-like in appearance.
• Just commands that take Tcl scripts as arguments.
• Example list reversal. Set list b to reverse of
  list a
• set b ""set i expr llength a - 1while i
  gt 0 lappend b lindex a i incr i
  -1
• Commands
• if for switch break
• foreach while eval continue
• source

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Control Structure Examples

• if expr script
• for script expr script script
• for set i 0 ilt10 incr i ...
• switch (opt) string p1 s1 p2 s2...
• foreach name my_name_list
• switch -regexp name
• Pete incr pete_count
• BobRobert incr bob_count
• default incr other_count

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More on Control Structures

• Brackets are never required - so watch out!
• set x 3
• if xgt2 ... lt this is OK, evaled once
• while xgt2 ... lt this is NOT OK, evaled
• 
  many times!
• set a red blue green
• foreach i a lt this is OK
• foreach i red blue green ...
• 
  NOT OK!
• foreach i array names A is a common idiom

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Procedures

• proc command defines a procedure
• proc sub1 x expr x-1
• Procedures behave just like built-in commands
• sub1 3 ? 2
• Arguments can have default values
• proc decr x y 1
• expr x-y

name
body
list of argument names
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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
• gt set x 10
• gt proc deltax d
• set x expr x-d
• gt deltax 1 gt can't read x no such variable
• gt proc deltax d
• global x
• set x expr x-d
• gt deltax 1 gt 9

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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
• 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 var1

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Procedures and Scope

• uplevel does for code what upvar does for
  variables
• proc loop from to script
• set i from
• while i lt to
• uplevel script
• incr i
• set s ""
• loop 1 5 set s s
• puts s gt

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More about Procedures

• Variable-length argument lists
• proc sum args set s 0
• foreach i args incr s i
  return s
• sum 1 2 3 4 5
• ? 15
• sum? 0

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Errors

• Errors normally abort commands in progress,
  application displays error message
• set n 0foreach i 1 2 3 4 5 set n expr
  n ii? syntax error in expression "n
  ii"
• Global variable errorInfo provides stack trace
• set errorInfo? syntax error in expression "n
  ii" while executing"expr n ii"
  invoked from within"set n expr n ii..."
  ("foreach" body line 2) ...

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Advanced Error Handling

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

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Tcl File I/O

• Tcl file I/O commands
• open gets seek flush globclose read tell cd fcon
  figure fblocked fileeventputs source eof pwd fi
  lename
• File commands use 'tokens' to refer to files
• set f open "myfile.txt" "r"
• gt file4
• puts f "Write this text into file"
• close f

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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
• gt (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
• gt (bytes 1024-1123 of file f)

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Tcl File I/O

• fileevent lets you watch a file
• set f open log r
• fileevent f readable \
• set data read f puts f
• Doesn't seem to work right on Windows NT, others?
• fblocked, fconfigure give you control over files
• fconfigure -buffering linefull
• fconfigure -blocking truefalse
• fconfigure -translation autobinarycrlfcrlf
• fblocked returns boolean

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TCP, Ports, and Sockets

• Networking uses layers of abstractions
• In reality, there is current on a wire...
• The Internet uses the TCP/IP protocol
• Abstractions
• IP Addresses (146.246.245.226)
• Port numbers (80 for WWW, 25 for SMTP)
• Sockets are built on top of TCP/IP
• Abstraction
• Listening on a port for connections
• Contacting a port on some machine for service
• Tcl provides a simplified Socket library

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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
• gt loads of HTML from Sun's home page
• Network looks just like a file!
• To create a server socket, just use
• socket -server accept portno

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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

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Runtime Information Facilities

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

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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

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Some More Interesting Tcl Features

• 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

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Tcl 7.6 and Tk 4.2

• 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).
• No other changes except bug fixes.
• Now in beta release final release in late
  September.

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For Next Week...

• 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!

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For Next Week...

• Programming assignment 1
• 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...
• Read Chapters 6 through 13 and 15 of Ousterhout