3.2 BASIC TCL RULES

This section specifies the rules for composing TCL command strings.

3.2.1 TCL Command String

A TCL command line is structured as follows:

    label> command-text       !comment

• The label is a command line label; it is allowed only on the first physical line of a command string and is terminated by ">"

• The "command-text" follows the rules for proc invocation described in the "TAE Command Language (TCL) User's Manual," or follows a rule particular to the command. Section 3.4 describes the proper form for each command.

• "!" introduces a comment; comments are ignored by TAE.

• If the command string cannot fit on one line, the line may be continued onto another using a "+" as the last non-comment, unquoted character. The continuation character is permitted any place in a command string where a space is allowed.

All fields, including the command text itself, are optional, and blank lines are ignored.

Examples:

  IMGCOPY FROM=IN TO=OUT   !Simple copy

  START> IMOCOPY FROM=IN TO=OUT   !Simple copy

  VECMUL (1, 2, 3, 4, 5) +  !Vector multiply
         (5, 6, 7, 8, 9)    !Continued line

3.2.2 Name Rules

A "name" in TCL is a character string used to refer to procs, files, labels, libraries, variables, and functions.

3.2.2.1 TCL Standard Names

AND
OR
NOT
_HELPVU
_PANEL
_TYPE
_MESSAGE
Implicit variables listed in Section 3.3.2.7.

In general, programmers should avoid names beginning with a dollar sign ($) or an underscore (_).

3.2.2.2 Library Names

TAE library names are host-dependent. For example, under VAX/VMS implementations of TAE, library names are directory names or logical names assigned to directory names; under UNIX implementations, a library name is the path name of a directory or a shell symbol (introduced with "$") whose value is a directory path name. See Appendix A to the "TAE Command Language (TCL) User's Manual" for library naming conventions for a given host.

3.2.2.3 Proc Names

A valid proc name is one of the following:

• a TCL standard name

• a host file name (See "File Names," below.)

  The proc names in Table 3-1 are reserved for use by TCL.

  3.2.2.4 File Names

  A file name in TCL is a host file specification. File specifications containing special characters may have to be quoted, depending on the host. See Appendix A to the "TAE Command Language (TCL) User's Manual."

  The value of a FILE type parameter is verified by TAE as follows: if, on the PARM command, the ACCESS is IN or INOUT, then the file identified by the value string must exist. (See Section 3.4.2 for a description of the PARM command.)

  File verification may be optionally turned on or off. (See Section 3.3.2.7.1 for the TAE GLOBAL $FILEVER). If verification is "off", no verification is performed and file type variables become identical to string type variables.

  3.2.3 Additional Syntax Rules

  3.2.3.1 Case Sensitivity

  The rules for TCL interpretation of uppercase versus lowercase strings are:

  1. TCL names are interpreted identically whether the characters used are uppercase or lowercase.

  2. In UNIX implementations of TAE, file name references, including proc names, are translated to lowercase before file access is attempted, unless the DISABLE-FORCE_LOWER command has been executed.

  3. The case of string values in parameters is maintained when the value is passed to a proc, except when acceptable values are specified with the VALID attribute of the PARM command.

     If the acceptable string values for a parameter are specified with the VALID attribute, then a user-entered value may differ in case, but the value passed to the proc will be exactly one of the values in the VALID list.

  4. An uppercase string and a lowercase string that are otherwise identical are considered to be "equal" when tested in a relational expression.

  5. The case of the value of the local variable _SUBCMD is the case of the subcommand definition (not the case used in the proc invocation).

  3.2.3.2 Lists

  A "list" in TCL consists of a group of items separated by commas, white space, or a comma and white space. "Whitespace" is one or more spaces and/or tabs.

  Examples:

  a, b, c,          !Three items
  a b c             !Three items
  a, b c            !Three items
  a, bc             !Two items
  

  NOTE: A list contained in an expression (as in a LET command) must use commas as separators.

  3.2.4 Special Characters

  A special character is one that has a special meaning to TCL. The significance of any special character, except "&", is lost if the character appears in a string contained between quotation marks. The quotation mark character loses its significance within a quoted string if it is immediately preceded by another quotation mark. Table 3-2 summarizes the use of special characters in TCL.

  The following punctuation characters are acceptable in a value field without quoting:

          / -- slash
          ; -- semi-colon
          . -- period
          [ -- bracket
          ] -- bracket
          - -- hyphen
          : -- colon
  

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  TABLE 3-2

  Summary of Special Character Use in TCL

  Character	Significance
  !	Introduces comments
  &	Substitution indicator
  &&	Literal ampersand (i.e., escape for &)
  *	1. Universal "here" indicator 2. Multiplication operator
  ()	1. Subscript indicator 2. Value list indicator 3. Delimiters for logical expressions 4. Function arguments indicator
  -	1. Binary subtraction operator 2. Unary negate 3. Subcommand indicator 4. In VMS, used in file specifications
  +	1. Continuation indicator 2. Binary addition operator 3. Unary positive
  =	1. Assignment operator 2. Relational equality operator
  <>	Relational inequality
  >=	Relational "greater than or equal to"
  <=	Relational "less than or equal to"
  >	1. Label terminator 2. Relational "greater than"
  <	Relational "less than"
  :	1. Separator in range specification 2. Used in VMS file specification
  "	Start or end of quoted string
  ""	Literal quotation mark (i.e., escape for when within a quoted string)
  |	Bracketing for command and parameter qualifiers
  //	String concatenation operator
  ,	Separator used in lists
  Spaces	General separator
  .	1. Separator in full parameter qualifier name 2. Decimal point in real values
  []	Reserved for RSX, VMS file specifications
  /	1. UNIX file specification separator 2. TCL division operator
  %	Host file escape
  ?	Last error message query (HELP-MESSAGE)
  '	(Apostrophe) Used to flag keyword values
  @	De-reference indicator

  
  

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