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Tcl(3tcl) Tcl Built-In Commands Tcl(3tcl) 





NAME


Tcl - Tool Command Language






SYNOPSIS


Summary of Tcl language syntax.








DESCRIPTION


The following rules define the syntax and semantics of the Tcl
    language:



  
[1] Script.

  
A script is composed of zero or more commands delimited by semi-colons or
      newlines.

  
[2] Command.

  
A command is composed of zero or more words delimited by whitespace. The
      replacement for a substitution is included verbatim in the word. For
      example, a space in the replacement is included in the word rather than
      becoming a delimiter, and \\ becomes a single backslash in the
      word. Each word is processed from left to right and each substitution is
      performed as soon as it is complete. For example, the command










set y [set x 0][incr x][incr x]




is composed of three words, and sets the value of y to
    012.


If hash (“#”) is the first character of what would
    otherwise be the first word of a command, all characters up to the next
    newline are ignored.





  
[3] Braced word.

  
If a word is enclosed in braces (“{”) and
      (“}”) , the braces are removed and the enclosed characters
      become the word. No substitutions are performed. Nested pairs of braces
      may occur within the word. A brace preceded by an odd number of
      backslashes is not considered part of a pair, and neither brace nor the
      backslashes are removed from the word.

  
[4] Quoted word.

  
If a word is enclosed in double quotes (“"”) , the
      double quotes are removed and the enclosed characters become the word.
      Substitutions are performed.

  
[5] List.

  
A list has the form of a single command. Newline is whitespace, and
      semicolon has no special interpretation. There is no script evaluation so
      there is no argument expansion, variable substitution, or command
      substitution: Dollar-sign and open bracket have no special interpretation,
      and what would be argument expansion in a script is invalid in a
    list.

  
[6] Argument expansion.

  
If “{*}” prefixes a word, it is removed. After any remaining
      enclosing braces or quotes are processed and applicable substitutions
      performed, the word, which must be a list, is removed from the command,
      and in its place each word in the list becomes an additional word in the
      command. For example,






cmd a {*}{b [c]} d {*}{$e f {g h}}



is equivalent to



cmd a b {[c]} d {$e} f {g h} .





  
[7] Evaluation.

  
To evaluate a script, an interpreter evaluates each successive command.
      The first word identifies a procedure, and the remaining words are passed
      to that procedure for further evaluation. The procedure interprets each
      argument in its own way, e.g. as an integer, variable name, list,
      mathematical expression, script, or in some other arbitrary way. The
      result of the last command is the result of the script.

  
[8] Command substitution.

  
Each pair of brackets (“[”) and (“]”) encloses
      a script and is replaced by the result of that script.

  
[9] Variable substitution.

  
Each of the following forms begins with dollar sign (“$”)
      and is replaced by the value of the identified variable. name names
      the variable and is composed of ASCII letters (A–Z
      and a–z), digits (0–9),
      underscores, or namespace delimiters (two or more colons). index is
      the name of an individual variable within an array variable, and may be
      empty.







  
$name

  
name may not be empty.
    

  

  
$name(index)

  
name may be empty. Substitutions are performed on
    index.

  
${name}

  
name may be empty.

  
${name(index)}

  
name may be empty. No substitutions are performed.





Variables that are not accessible through one of the forms above may be accessed
  through other mechanisms, e.g. the set command.


  
[10] Backslash substitution.

  
Each backslash (“\”) that is not part of one of the forms
      listed below is removed, and the next character is included in the word
      verbatim, which allows the inclusion of characters that would normally be
      interpreted, namely whitespace, braces, brackets, double quote, dollar
      sign, and backslash. The following sequences are replaced as
    described:











  

  
Audible alert (bell) (U+7).

  

  
Backspace (U+8).

  

  
Form feed (U+C).

  

  
Newline (U+A).

  

  
Carriage-return (U+D).

  

  
Tab (U+9).

  

  
Vertical tab (U+B).

  
\<newline>whiteSpace

  
Newline preceded by an odd number of backslashes, along with the
      consecutive spaces and tabs that immediately follow it, is replaced by a
      single space. Because this happens before the command is split into words,
      it occurs even within braced words, and if the resulting space may
      subsequently be treated as a word delimiter.

  
\\

  
Backslash (“\”).

  

  
Up to three octal digits form an eight-bit value for a Unicode character
      in the range 0–377, i.e. U+0–U+FF. Only the
      digits that result in a number in this range are consumed.

  

  
Up to two hexadecimal digits form an eight-bit value for a Unicode
      character in the range 0–FF.

  

  
Up to four hexadecimal digits form a 16-bit value for a Unicode character
      in the range 0–FFFF.

  

  
Up to eight hexadecimal digits form a 21-bit value for a Unicode character
      in the range 0–10FFFF. Only the digits that result in
      a number in this range are consumed.














KEYWORDS


backslash, command, comment, script, substitution, variable







  

    8.6
    Tcl