New in Tcl? Coming from another language? Read on.

This could be fun. I learned almost all of my programming with [PHP], and a little bit of [Perl]. This sheet [http://www.cs.tufts.edu/g/20/notes/php_perl.php] helped me an awful lot when I tried to learn [Perl], so a Tcl cheat sheet may be awfully useful to someone else. Feel free to add other languages.


How about we get the Tcl stuff correct before adding other languages? Roy Terry, 17Jan2003


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'''PHP:'''  file.php3

'''PERL:'''  file.cgi

'''TCL:'''  file.tcl
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'''PHP:'''  scripts in <?php..?>

'''PERL:'''  whole file is script

'''TCL:'''  whole file is script (unless you use mod_dtcl in Apache 1.3.x or mod_tcl/rivet in Apache 2.x, there everything is like PHP)
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'''PHP:'''  can include raw HTML

'''PERL:'''  must print all output

'''TCL:'''  must print all output (unless you use mod_dtcl in Apache 1.3.x or mod_tcl/rivet in Apache 2.x, there everything is like PHP)
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'''PHP:'''  no requirements for first line

'''PERL:'''  first line is #!/usr/local/bin/perl or any other path to your Perl interpreter (but is that a requirement?)

'''TCL:'''  first line can be #!/usr/local/bin/tclsh  or any other path to your Tcl interpreter (but that is absolutely irrelevant if you are using Windows). See [exec magic] for the recommended way to start a Tcl file if you want it to behave like an app on *nix systems.
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'''protections'''

'''PHP:'''  not executable file

'''PERL:'''  executable file

'''TCL:'''  What the heck? You can make almost any file executable in nix platforms!
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'''PHP:'''  chmod 644 file.php3

'''PERL:'''  chmod a+x file.cgi

'''TCL:'''  chmod a+x file.tcl
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'''printing'''

'''PHP:'''  echo "stuff\n";

'''PERL:'''  print "stuff\n";

'''TCL:'''  puts stuff  '''OR'''  puts "some stuff"  '''OR''' puts {some stuff}. It may be useful here to point out that Tcl adds a trailing newline by default. To disable this behaviour use the -nonewline option to puts.
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'''variables'''

'''PHP:'''  All variables $var

'''PERL:'''  $var is a scalar variable.

'''TCL:'''  '''var''' refers to the name of a variable which is needed every time you want to modify its contents (write to the variable); or '''$var''' referes to the content of the variable to be used when you want to read the variable . See [set]
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'''PHP:'''  $var always means one thing

'''PERL:'''  $var, @var, %var, var are different things!

'''TCL:'''  since all variables have a $var in front, $var always means the same thing. But beware: var could be scalar or an array variable and has to be used according to that!
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'''arrays'''

'''PHP:'''  $var = array(1,2,3);

'''PERL:'''  @var = (1,2,3);

'''TCL:'''  well, there are lists which work very fine, plus there are arrays (which are called hashes in some other languages), see below

 set var "1 2 3"  '''OR'''  set var [ list 1 2 3 ] while the latter is preferred especially in cases where the contents are not as simple as "1 2 3", but may contain spaces, return values from functions and so on. Only the list command helps you to correctly use quoting.

and arrays...

 array set var "key1 value1 key2 value2 key3 value3"

'''PHP:'''  "numeric" arrays and "associative" arrays

'''PERL:'''  "arrays" and "hashes"

'''TCL:'''  "lists" and associative "arrays" - of course the associative arrays can have numbers as indexes.

([NEM] and we now have [dict]s)

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'''PHP:'''  $var[[1]] is second element of $var

'''PERL:'''  $var[[1]] is second element of @var

'''TCL:'''  [[ lindex $var 1 ]] is second element of $var
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'''PHP:'''  count($var) is length

'''PERL:'''  scalar(@var) is length

'''TCL:'''  [[ llength $var ]] is length of list, and [llength [array names var]] is number of elements in array.
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'''PHP:'''  for ($i=0; $i<count($var); $i++) echo $var[[$i]];

'''PERL:'''  foreach $thing (@var) { print $thing; }

'''TCL:'''  for { set i 0 }  {$i < [[ llength $var ]] }  { incr i }  { puts [[ lindex $var $i ]] }

[NEM] This Tcl example would be far better written as: foreach thing $var { puts $thing }

Working through an array works like this: 

 foreach index [array names var] {
    puts $var($index)
 } ;# foreach

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'''PHP:'''  join(":",array(1,2,3))

'''PERL:'''  join(":",(1,2,3))

'''TCL:'''  join [[ list 1 2 3 ]] :   (yeah, yeah, you can wrap the colon in quotes if you're queasy)
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'''objects'''

'''PHP:'''  associative arrays are arrays

'''PERL:'''  associative arrays are their own type

'''TCL:'''  Er... what is a "type"?  ;-) If you like objects you could use [incr Tcl] or [stooop]
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'''PHP:'''  $var = array(1=>"ho","hi"=>4);

'''PERL:'''  %var = (1=>"ho","hi"=>4);

'''TCL:'''  array set var "1 ho hi 4"
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'''Access value of single array element 'ho' '''

'''PHP:'''  $var[['ho']] 

'''PERL:'''  $var{'ho'} 

'''TCL:'''  $var(ho) (for constants with no white space quotes not needed)
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'''PHP:'''  while (list($k,$v) = each $var)) {...}

'''PERL:'''  while (($k,$v) = each %var) {...}

'''TCL:'''  er...  foreach { key value } [[ array get var ]]  {...}
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'''to be continued...'''

Roy Terry, 17Jan2003 - say this looks helpful. On your next pass can you be more specific on 1) What each section is trying to
demonstrate, and 2) your questions about Tcl. "??? - confusing" doesn't give folks a good idea of what additional info you need.
One obvious correction: Tcl uses parens, not square brackets, to index arrays. Further more the single quote has absolutely no
special meaning in Tcl, it does not quote things and it will not be removed by the parser; so best to avoid it. Now I see something
else: In Tcl variables can be either an array or a string value and that's determined by usage.

[LES]: It's not Tcl that confuses me. It's the PHP and Perl examples that confused me, so I am not sure how to translate them into Tcl. For example: instead of saying '''$var[['ho']] is element indexed by 'ho' ''', I'd rather say '''"ho" is element indexed by $var[['1']]'''. Do I make myself clear?  RT - no I don't think you do. Take a look at the array access segment now. I think it helps
to put the "operation" at the top of the section and then just list the code sample.

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