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Tcl_Eval(3)		    Tcl Library Procedures		   Tcl_Eval(3)

______________________________________________________________________________

NAME
       Tcl_Eval,  Tcl_VarEval, Tcl_EvalFile, Tcl_GlobalEval - execute Tcl com‐
       mands

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 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 exe‐
       cuted.  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, con‐
       catenates 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  con‐
       tents  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_CON‐
       TINUE  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.

SEE ALSO
       Tcl_EvalObj, Tcl_GlobalEvalObj

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

Tcl				      7.0			   Tcl_Eval(3)
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