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     Tcl_Eval(3)		 Tcl (7.0)		   Tcl_Eval(3)

     _________________________________________________________________

     NAME
	  Tcl_Eval, Tcl_VarEval, Tcl_EvalFile, Tcl_GlobalEval -
	  execute Tcl commands

     SYNOPSIS
	  #include <tcl.h>

	  int
	  Tcl_Eval(interp, cmd)

	  int
	  Tcl_VarEval(interp, string, string, ... (char *) NULL)

	  int
	  Tcl_EvalFile(interp, fileName)

	  int
	  Tcl_GlobalEval(interp, cmd)

     ARGUMENTS
	  Tcl_Interp   *interp	    (in)      Interpreter in which to
					      execute the command.  A
					      string result will be
					      stored in interp-
					      >result.

	  char	       *cmd	    (in)      Command (or sequence of
					      commands) to execute.
					      Must be in writable
					      memory (Tcl_Eval makes
					      temporary modifications
					      to the command).

	  char	       *string	    (in)      String forming part of
					      Tcl command.

	  char	       *fileName    (in)      Name of file containing
					      Tcl command string.
     _________________________________________________________________

     DESCRIPTION
	  All four of these procedures execute Tcl commands.  Tcl_Eval
	  is the core procedure and is used by all the others.	It
	  executes the commands in the script held by cmd until either
	  an error occurs or it reaches the end of the script.

	  Note that Tcl_Eval and Tcl_GlobalEval have been largely
	  replaced by the object-based procedures Tcl_EvalObj and
	  Tcl_GlobalEvalObj.  Those object-based procedures evaluate a

     Page 1					     (printed 2/19/99)

     Tcl_Eval(3)		 Tcl (7.0)		   Tcl_Eval(3)

	  script held in a Tcl object instead of a string.  The object
	  argument can retain the bytecode instructions for the script
	  and so avoid reparsing the script each time it is executed.
	  Tcl_Eval is implemented using Tcl_EvalObj but is slower
	  because it must reparse the script each time since there is
	  no object to retain the bytecode instructions.

	  The return value from Tcl_Eval is one of the Tcl return
	  codes TCL_OK, TCL_ERROR, TCL_RETURN, TCL_BREAK, or
	  TCL_CONTINUE, and interp->result will point to a string with
	  additional information (a result value or error message).
	  If an error occurs during compilation, this return
	  information describes the error.  Otherwise, this return
	  information corresponds to the last command executed from
	  cmd.

	  Tcl_VarEval takes any number of string arguments of any
	  length, concatenates them into a single string, then calls
	  Tcl_Eval to execute that string as a Tcl command.  It
	  returns the result of the command and also modifies interp-
	  >result in the usual fashion for Tcl commands.  The last
	  argument to Tcl_VarEval must be NULL to indicate the end of
	  arguments.

	  Tcl_EvalFile reads the file given by fileName and evaluates
	  its contents as a Tcl command by calling Tcl_Eval.  It
	  returns a standard Tcl result that reflects the result of
	  evaluating the file.	If the file couldn't be read then a
	  Tcl error is returned to describe why the file couldn't be
	  read.

	  During the processing of a Tcl command it is legal to make
	  nested calls to evaluate other commands (this is how
	  procedures and some control structures are implemented).  If
	  a code other than TCL_OK is returned from a nested Tcl_Eval
	  invocation, then the caller should normally return
	  immediately, passing that same return code back to its
	  caller, and so on until the top-level application is
	  reached.  A few commands, like for, will check for certain
	  return codes, like TCL_BREAK and TCL_CONTINUE, and process
	  them specially without returning.

	  Tcl_Eval keeps track of how many nested Tcl_Eval invocations
	  are in progress for interp.  If a code of TCL_RETURN,
	  TCL_BREAK, or TCL_CONTINUE is about to be returned from the
	  topmost Tcl_Eval invocation for interp, it converts the
	  return code to TCL_ERROR and sets interp->result to point to
	  an error message indicating that the return, break, or
	  continue command was invoked in an inappropriate place.
	  This means that top-level applications should never see a
	  return code from Tcl_Eval other then TCL_OK or TCL_ERROR.

     Page 2					     (printed 2/19/99)

     Tcl_Eval(3)		 Tcl (7.0)		   Tcl_Eval(3)

     SEE ALSO
	  Tcl_EvalObj, Tcl_GlobalEvalObj

     KEYWORDS
	  command, execute, file, global, object, object result,
	  variable

     Page 3					     (printed 2/19/99)

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