NAME
       Tcl - Tool Command Language

SYNOPSIS
       Summary of Tcl language syntax.

DESCRIPTION
       The  following  rules  define  the syntax and semantics of the Tcl lan-
       guage:

       [1] Commands.
              A Tcl script is a string containing one or more commands.  Semi-
              colons  and  newlines  are  command  separators unless quoted as
              described below.  Close brackets are command terminators  during
              command substitution (see below) unless quoted.

       [2] Evaluation.
              A command is evaluated in two steps.  First, the Tcl interpreter
              breaks the command into  words  and  performs  substitutions  as
              described  below.  These substitutions are performed in the same
              way for all commands.  The first word is used to locate  a  com-
              mand  procedure  to carry out the command, then all of the words
              of the command are passed to the command procedure.  The command
              procedure  is  free to interpret each of its words in any way it
              likes, such as an integer, variable name, list, or  Tcl  script.
              Different commands interpret their words differently.

       [3] Words.
              Words of a command are separated by white space (except for new-
              lines, which are command separators).

       [4] Double quotes.
              If the first character of a word is  double-quote  (``"'')  then
              the  word  is terminated by the next double-quote character.  If
              semi-colons, close brackets, or white space characters  (includ-
              ing newlines) appear between the quotes then they are treated as
              ordinary characters and included in the word.  Command substitu-
              tion, variable substitution, and backslash substitution are per-
              formed on the characters between the quotes as described  below.
              The double-quotes are not retained as part of the word.

       [5] Braces.
              If  the  first character of a word is an open brace (``{'') then
              the word is terminated by  the  matching  close  brace  (``}'').
              Braces  nest  within  the  word:  for each additional open brace
              there must be an additional close brace  (however,  if  an  open
              brace  or close brace within the word is quoted with a backslash
              then it is not counted in locating the  matching  close  brace).
              No  substitutions  are  performed  on the characters between the
              braces  except  for  backslash-newline  substitutions  described
              below,  nor  do  semi-colons, newlines, close brackets, or white
              space receive any special interpretation.  The word will consist
              of  exactly the characters between the outer braces, not includ-
              ing the braces themselves.

       [6] Command substitution.
              If a word contains an open bracket  (``['')  then  Tcl  performs
              command substitution.  To do this it invokes the Tcl interpreter
              recursively to process the characters following the open bracket
              as  a Tcl script.  The script may contain any number of commands
              and must be terminated by a close bracket (``]'').   The  result
              of  the  script (i.e. the result of its last command) is substi-
              tuted into the word in place of the  brackets  and  all  of  the
              characters  between  them.   There  may be any number of command
              substitutions in a single word.   Command  substitution  is  not
              performed on words enclosed in braces.

       [7] Variable substitution.
              If  a word contains a dollar-sign (``$'') followed by one of the
              forms described below, then Tcl performs variable  substitution:
              the dollar-sign and the following characters are replaced in the
              word by the value of a variable.  Variable substitution may take
              any of the following forms:

              $name          Name  is the name of a scalar variable;  the name
                             is a sequence of one or more characters that  are
                             a letter, digit, underscore, or namespace separa-
                             tors (two or more colons).

              $name(index)   Name gives the name  of  an  array  variable  and
                             index  gives  the  name of an element within that
                             array.  Name must contain only  letters,  digits,
                             underscores, and namespace separators, and may be
                             an empty string.  Command substitutions, variable
                             substitutions,  and  backslash  substitutions are
                             performed on the characters of index.

              ${name}        Name is the name of a scalar  variable.   It  may
                             contain  any  characters  whatsoever  except  for
                             close braces.

              There may be any number of variable substitutions  in  a  single
              word.   Variable substitution is not performed on words enclosed
              in braces.

       [8] Backslash substitution.
              If a backslash (``\'') appears within a word then backslash sub-
              stitution  occurs.   In  all cases but those described below the
              backslash is dropped and the following character is  treated  as
              an  ordinary  character  and  included in the word.  This allows
              characters such as double quotes,  close  brackets,  and  dollar
              signs  to  be  included in words without triggering special pro-
              cessing.  The following table lists the backslash sequences that
              are  handled  specially, along with the value that replaces each
              sequence.

              \a     Audible alert (bell) (0x7).

              \b     Backspace (0x8).

              \f     Form feed (0xc).

              \n     Newline (0xa).

              \r     Carriage-return (0xd).

              \t     Tab (0x9).

              \v     Vertical tab (0xb).

              \<newline>whiteSpace
                     A single space character replaces the backslash, newline,
                     and  all  spaces  and tabs after the newline.  This back-
                     slash sequence is unique in that it is replaced in a sep-
                     arate  pre-pass  before  the  command is actually parsed.
                     This means that it will be replaced even when  it  occurs
                     between  braces,  and the resulting space will be treated
                     as a word separator if it isn't in braces or quotes.

              \\     Backslash (``\'').

              \ooo   The digits ooo (one, two,  or  three  of  them)  give  an
                     eight-bit octal value for the Unicode character that will
                     be inserted.  The upper bits  of  the  Unicode  character
                     will be 0.

              \xhh   The  hexadecimal  digits hh give an eight-bit hexadecimal
                     value for the Unicode character that  will  be  inserted.
                     Any number of hexadecimal digits may be present; however,
                     all but the last two are ignored (the result is always  a
                     one-byte  quantity).  The upper bits of the Unicode char-
                     acter will be 0.

              \uhhhh The hexadecimal digits hhhh (one, two, three, or four  of
                     them)  give  a sixteen-bit hexadecimal value for the Uni-
                     code character that will be inserted.

              Backslash substitution is not performed  on  words  enclosed  in
              braces, except for backslash-newline as described above.

       [9] Comments.
              If  a  hash  character  (``#'')  appears at a point where Tcl is
              expecting the first character of the first word  of  a  command,
              then  the  hash  character and the characters that follow it, up
              through the next newline, are treated as a comment and  ignored.
              The  comment  character only has significance when it appears at
              the beginning of a command.

       [10] Order of substitution.
              Each character is processed exactly once by the Tcl  interpreter
              as  part  of  creating  the words of a command.  For example, if
              variable substitution occurs then no further  substitutions  are
              performed  on  the value of the variable;  the value is inserted
              into the word verbatim.  If command substitution occurs then the
              nested  command  is  processed entirely by the recursive call to
              the Tcl interpreter; no substitutions are performed before  mak-
              ing  the recursive call and no additional substitutions are per-
              formed on the result of the nested script.

              Substitutions take place from left to right, and each  substitu-
              tion  is  evaluated completely before attempting to evaluate the
              next.  Thus, a sequence like
                     set y [set x 0][incr x][incr x]
              will always set the variable y to the value, 012.

       [11] Substitution and word boundaries.
              Substitutions do not affect the word boundaries  of  a  command.
              For  example,  during  variable substitution the entire value of
              the variable becomes part of a single word, even  if  the  vari-
