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Programming Using Tcl/TkWeek 2
Seree Chinodom
http://lecture.compsci.buu.ac.th/TclTk
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
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 you’d especially like to see covered
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!
More On Substitutions
Keep substitutions simple: use commands like format for complex arguments.
Use eval for another level of expansion:
exec rm *.oํ *.o: No such file or directory
*glob .oํ a.o b.o
[*. ]ํ a.o b.o: No such file or directory
*eval exec rm [glob .o]
Tcl Expressions C-like (int and double) Command, variable substitution occurs within expressions. Used in eeee, if, other commands.
Sample command Resultset b 5 5expr ($b*4) - 3 17expr $b <= 2 0expr $a * cos(2*$b) -5.03443expr {$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!
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
=> 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!)
Tcl Expressions
What’s happening in these expressions?expr $a * cos(2*$b) -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 \$aset a 4expr $b * 2 8
Tcl String Expressions
Some Tcl operators work on strings too
set a Bill Billexpr {$a < "Anne"} 0
<, >, <=, >=, ==, and != work on strings
Beware when strings can look like numbers
You can also use the string compare function
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 lsearchforeach linsert lrange lsortlappend list lreplace
Note: all indices start with 0. end means last element Examples:
lindex {a b {c d e} f} 2 ํ c d elsort {red green blue} ํ blue green red
Lists are Powerful
A list makes a handy stack
Sample command Resultset stack 1 1push stack red red 1push stack {a fish} {a fish} red 1pop stack a fish (stack is now red 1)
push and pop are very short and use list commands to do their work
More about Lists
A true list’s meaning won’t change when (re)scanned
red $animal blue $animal <= not a listred fish blue fish <= list
red \$fish blue \$fish <= not a list, but
list red \$fish blue \$fish gives you…
red {$fish} blue {$fish} <= which is a list
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 Lists parse cleanly as commands: each element becomes
one 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 $initValue](always works: if initValue is "{" command is " set x \{")
List commands do all the work for you!
String Manipulation
String manipulation commands:
regexp format split string
regsub scan join eeeeee subcommands
compare first last index length
match range toupper tolower trim
trimleft trimright Note: all indexes start with 0. end means last char
Globbing & Regular Expressions "Globbing" - a simple pattern language
– * means any sequence of characters
– ? matches any one character
– [chars] matches and one character in chars
– \c matches c, even if c is *, [, ?, etc. Good for filename matching
– *.exe , [A-E]*.txt, \?*.bak glob command applies a glob pattern to filenames
foreach f [glob *.exe] {
puts "$f is a program"
}
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.
Globbing & Regular Expressions Examples:
[A-Za-z0-9_]+ : valid Tcl identifiers
T(cl|k) : Tcl or Tk regexp commandregexp T(cl|k) "I mention Tk" w t=> returns 1 (match), w becomes "Tk", t gets "k"
regsub commandregsub -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#: #148766207"
scan $x "SSN#: %d" ssn
puts "The social security number is $ssn"
=> The social security number is 148766207
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 $a] - 1]while {$i >= 0} { lappend b [lindex $a $i] incr i -1}
Commands:if for switch breakforeach while eval continuesource
Control Structure Examples
if expr script for script expr script script
for {set i 0} {$i<10} {incr i} {... 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 Brackets are never required - so watch out!
3set x
>2 {... <= this is OK, eval’ed once
>2 {... <= this is NOT OK, eval’ed
many times!
eeee eeee eeeeee{} 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}
Procedures behave just like built-in commands:sub1 3 ํ 2
Arguments can have default values:proc decr {x {y 1}} { expr $x-$y}
name
list of argument names
body
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 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 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
Variable-length argument lists:proc sum args { set s 0 foreach i $args { incr s $i } return $s}
sum 1 2 3 4 5ํํํํํํํํํํํํํํ 15sumํ 0
Errors Errors normally abort commands in progress, applicati
on displays error message:set n 0foreach i {1 2 3 4 5} { set n [expr {$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 eeeee value).
NONE (in this case) Can intercept errors (like exception handling):
catch {expr {2 +}} msgํ 1 (catch returns 0=OK, 1=err, other values...)
eee eeeํ ee ee"2+"
You can generate errors yourself (style question:)
error "bad argument"
- return code error "bad argument"
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
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)
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 [line|full]
fconfigure -blocking [true|false]
fconfigure -translation [auto|binary|cr|lf|crlf]
fblocked returns boolean
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
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]
=> 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
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
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
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 Autoloading:
– unknow n 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
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.
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!
For Next Week...
Programming assignment #1 Try to check out the Netscape Plug-in Buy the reader and find pages about commands introd
uced since Ousterhout was published: fileevent, socket, fconfigure, interp, others...
Read Chapters 6 through 13 and 15 of Ousterhout
