Tcl Programming/TCL and ADP

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Tcl and ADP Reference

This is a reference for using Tcl with ADP pages, for people setting up a site with the ArsDigita Community System (see OpenACS for details). The first half is just a Tcl overview; the second half deals with .adp pages, custom tags, and AOLServer resources and parameters.

Tcl Overview

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Basic Tcl Language Features

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; or newline statement separator
\ statement continuation if last character in line
# comment out rest of line (if 1st non−whitespace char)
var simple variable
var(index) associative array variable
var(i,j) multidimensional associative array variable
$var variable substitution (also ${var}xyz)
[expr 1+2] command substitution
\char backslash substitution
"hello $a" quoting with substitution
{hello $a} quoting with no subst (deferred substitution)

The only datatype in Tcl is a string. Some commands interpret arguments as numbers/booleans; those formats are:'
Integer: 12 0xff(hex) 0377(octal)
Floating Pt: 2.1 3. 6e4 7.91e+16
Boolean: true false 0 1 yes no

Backslash Substitutions

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\a audible alert (0x7)
\b backspace (0x8)
\f form feed (0xC)
\n newline (0xA)
\r carriage return (0xD)
\t horizontal tab (0x9)
\v vertical tab (0xB)
\space space
\newline space
\ddd octal value (d=0−7)
\xdd hex value (d=0−9,a−f)
\c replace ’\c’ with ’c’
\\ backslash

Operators and Math Functions

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The expr command recognizes these operators, in decreasing order of precedence:

− ~ ! unary minus, bitwise NOT, logical NOT
* / % multiply, divide, remainder
+ − add, subtract
<< >> bitwise shift left, bitwise shift right
< > <= >= boolean comparisons
== != boolean equals, not equals
& bitwise AND
^ bitwise exclusive OR
| bitwise inclusive OR
&& logical AND
|| logical OR
x ? y : z if x != 0, then y, else z

All operators support integers. All support floating point except : ~, %, <<, >>, %, ^, and |. Boolean operators can also be used for string operands, in which case string comparison will be used. This occurs if any of the operands are not valid numbers. The following operators have "lazy evaluation" as in C:
&&, ||, ?:
The expr command recognizes the following math functions:
abs hypot int double floor ceil fmod round
cos sin tan acos asin atan atan2 cosh sinh tanh
log log10 exp pow sqrt

Regular Expressions

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regex | regex match either expression
regex* match zero or more of regex
regex+ match one or more of regex
regex? Match zero or one of regex
. any single character except newline
^ match beginning of string
$ match end of string
\c match character c
c match character c
[abc] match set of characters
[^abc] match characters not in set
[a−z] match range of characters
[^a−z] match characters not in range
( ) group expressions

Pattern Globbing

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? match any single character
* match zero or more characters
[abc] match set of characters
[a−z] match range of characters
\c match character c
{a,b,...} match any of string a, b, etc.
~ home directory (for glob command)
~user match user’s home directory (for glob command)
Note: for the glob command, a "." at the beginning of a file’s
name or just after "/" must be matched explicitly and all "/"
characters must be matched explicitly.

Control Flow

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Abort innermost containing loop command
Obsolete, see switch
Skip to next iteration of innermost containing loop.
Terminate the process, return returnCode (an integer which
defaults to 0) to the system as the exit status.
for start test next body
Looping command where start, next, and body are Tcl command
strings and test is an expression string to be passed to expr
foreach varname list body
The Tcl command string body is evaluated for each item in the
string list where the variable varname is set to the item’s value.
if expr1 [then] body1 [elseif expr2 [then] body2...] [[else] bodyN]
If expression string expr1 evaluates true, Tcl command string
body1 is evaluated. Otherwise if expr2 is true, body2 is
evaluated, and so on. If none of the expressions evaluate to
true, then bodyN is executed.
return [−code code] [−errorinfo info] [−errorcode code] [string]
Return immediately from current procedure with string as return
switch [options] string pattern1 body1 [ pattern2 body2 ...]
The string argument is matched against each of the pattern
arguments in order. As soon as it finds a pattern that matches
string, it evaluates the corresponding Tcl command string body. If
no match is found and the last pattern is the keyword default, its
command string is evaluated
while test body
Evaluates the Tcl command string body as long as expression string
test evaluates to true.


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Note: list indices start at 0 and the word end may be used to reference the last element in the list.

concat [arg arg ...]
Returns concatenation of each string
join list [joinString]
Returns string created by joining all elements of list with
lappend varName [value value ...]
Appends each value to the end of the list stored in varName.
lindex list index
Returns value of element at index in list.
linsert list index element [element ...]
Returns new list formed by using each arg as an element.
llength list
Returns number of elements in list.
lrange list first last
Returns new list from slice of list at indices first through last
lsearch [mode] list pattern
Returns index of first element in list that matches pattern (−1
for no match). Mode may be −exact, −glob(default) or −regexp.
lsort [switches] list
Returns new list formed by sorting list according to switches.
These are:
−ascii string comparison (default)
−integer integer comparisons
−real floating−point comparisons
−increasing sort in increasing order (default)
−decreasing sort in decreasing order
−command cmd Use command which takes two arguments and returns
an integer less than, equal to, or greater than zero.
split string [splitChars]
Returns a list formed by splitting string at each character in


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append varName [value value ...]
Appends each of the given values to the string stored in varName.

format formatString [arg arg ...]
Returns a formatted string generated in the ANSI C sprintf manner.

regexp [switches] exp string [matchVar] [subMatchVar ...]
Returns 1 if the regular expression exp matches part or all of
string, 0 otherwise. If specified, matchVar will be wet to all
the characters in the match and the following subMatchVar’s will
be set to matched parenthesized subexpressions. The −nocase
switch can be specified to ignore case in matching. The −indices
switch can be specified so that matchVar and subMatchVar will be
set to the start and ending indice3s in string of their
corresponding match.

regsub [switches] exp string subSpec varName
Replaces the first portion of string that matches the regular
expression exp with subSpec and places results in varName. Returns
count of number of replacements made. The −nocase switch can be
specified to ignore case in matching. The −all switch will cause
all matches to be substituted for.

scan string formatString varName [varName ...]
Extracts values into given variables using ANSI C sscanf behavior.
string compare string1 string2
Return −1, 0, or 1, depending on whether string1 is
lexicographically less than, equal to, or greater than string2.
string first string1 string2
Return index in string2 of first occurrence of string1 (−1 if not

string index string charIndex
Returns the charIndex’th character in string.

string last string1 string2
Return index in string2 of last occurrence of string1 (−1 if not

string length string
Returns number of characters in string.

string match pattern string
Returns 1 if glob pattern matches string, 0 otherwise.

string range string first last
Returns characters from string at indices first through last

string tolower string
Returns new string formed by converting all chars in string to
lower case.

string toupper string
Returns new string formed by converting all chars in string to
upper case.

string trim string [chars]
Returns new string formed by removing from string any leading or
trailing characters present in the set chars.

string trimleft string [chars]
Same as string trim for leading characters only.

string trimright string [chars]
Same as string trim for trailing characters only.

string wordend string index
Returns index of character just after last one in word at index in

string wordstart string index
Returns index of first character of word at index in string.

subst [−nobackslashes] [−nocommands] [−novariables] string
Returns result of backslash, command, and variable substitutions
on string. Each may be turned off by switch.

The Tcl <--> ADP interface

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Including TCL code in ADP pages

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Inline replacement: <%= tcl code that evaluates to the text you want embedded %>

State changing Code: <% tcl commands to change tcl environment (set vars, do db queries, etc) %>

Example: Two plus two is <%= [expr 2+2] %>

Defining custom tags

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ns_register_adptag "codeexample" "/codeexample" tcl_adp_codeexample

proc tcl_adp_codeexample {string tagset} {
return "<blockquote>

Using AOLServer Parameters

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[ad_parameter UsersCanCreateRoomsP chat]

Resourcing tcl in AOLserver

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source−file.tcl − to source a particular file.

ns_eval [list source $file]
ns_return 200 text/html ok
wget −O − "http://localhost:8000/source−

Note: this does not work for registered tag changes. To cause a reload of everything:

set dir [ns_info tcllib]
set list [exec ls $dir]
foreach file $list {
source $dir/$file
ns_puts "sourced: $file

Using ns_set

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When one queries a database, the variable that is set is an ns_set:

# ask AOLserver to give us a database connection
set db [ns_db gethandle]
set sql_query "select first_names, last_name
from users
where user_id = $user_id"
# actually send the query to the RDBMS; tell AOLserver we
# expect exactly one row back
set selection [ns_db 1row $db $sql_query]
''Getting information out of an ns_set:''
set first_names [ns_set get $selection "first_names"]
set last_name [ns_set get $selection "last_name"]
ns_return 200 text/plain "User #$user_id is $first_names $last_name"

Dealing with Form Variables

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Importing form variables into a tcl or adp page set_the_usual_form_variables Manipulating Forms Directly: ns_getform


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Do logic w/o breaking out of an ns_write. Just like SQL ! [util_decode unknown val1 res1 val2 res2 valN resN defaultresult]

Dealing With .ini file Parameters

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ad_parameter ad_parameter name { subsection "" } { default "" }

Returns the value of a configuration parameter set in one of the .ini files in
/web/yourdomain/parameters. If the parameter doesn’t exist, returns the
default specified as the third argument (or empty string if not default is
specified). Note that AOLserver reads these files when the server starts up and
stores parameters in an in−memory hash table. The plus side of this is that
there is no hit to the file system and no need to memoize a call to
ad_parameter. The minus side is that you have to restart the server if you
want to test a change made to the .ini file.

ad_parameter_section ad_parameter_section { subsection "" }

Returns all the vars in a parameter section as an ns_set. Relies on
undocumented AOLserver Tcl API call ns_configsection (analogous C API
call is documented). Differs from the API call in that it returns an empty
ns_set if the parameter section does not exist.

Converting tcl to adp

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inclusion of sub−files

# Source user−new.adp. We would redirect to it, but we don’t want
# the password exposed!
# source "[ns_url2file "/register/user−new.tcl"]"
# return
ns_adp_include user−new.adp