This document is a Mac OS X manual page. Manual pages are a command-line technology for providing documentation. You can view these manual pages locally using the man(1) command. These manual pages come from many different sources, and thus, have a variety of writing styles.

For more information about the manual page format, see the manual page for manpages(5).

uplevel(n)                                  Tcl Built-In Commands                                 uplevel(n)



____________________________________________________________________________________________________________

NAME
       uplevel - Execute a script in a different stack frame

SYNOPSIS
       uplevel ?level? arg ?arg ...?
____________________________________________________________________________________________________________


DESCRIPTION
       All  of  the  arg arguments are concatenated as if they had been passed to concat; the result is then
       evaluated in the variable context indicated by level.  Uplevel returns the result of that evaluation.

       If  level is an integer then it gives a distance (up the procedure calling stack) to move before exe-cuting executing
       cuting the command.  If level consists of # followed by a number then the number  gives  an  absolute
       level  number.   If  level  is omitted then it defaults to 1.  Level cannot be defaulted if the first
       command argument starts with a digit or #.

       For example, suppose that procedure a was invoked from top-level, and that it called b,  and  that  b
       called  c.   Suppose  that  c invokes the uplevel command.  If level is 1 or #2  or omitted, then the
       command will be executed in the variable context of b.  If level is 2 or #1 then the command will  be
       executed in the variable context of a.  If level is 3 or #0 then the command will be executed at top-level toplevel
       level (only global variables will be visible).

       The uplevel command causes the invoking procedure to disappear from the procedure calling stack while
       the command is being executed.  In the above example, suppose c invokes the command
              uplevel 1 {set x 43; d}
       where  d  is another Tcl procedure.  The set command will modify the variable x in b's context, and d
       will execute at level 3, as if called from b.  If it in turn executes the command
              uplevel {set x 42}
       then the set command will modify the same variable x in b's context:  the procedure c does not appear
       to  be  on  the call stack when d is executing.  The command ``info level'' may be used to obtain the
       level of the current procedure.

       Uplevel makes it possible to implement new control constructs as Tcl procedures (for example, uplevel
       could be used to implement the while construct as a Tcl procedure).

       namespace  eval  is another way (besides procedure calls) that the Tcl naming context can change.  It
       adds a call frame to the stack to represent the namespace context.  This means  each  namespace  eval
       command  counts as another call level for uplevel and upvar commands.  For example, info level 1 will
       return a list describing a command that is either the  outermost  procedure  call  or  the  outermost
       namespace  eval command.  Also, uplevel #0 evaluates a script at top-level in the outermost namespace
       (the global namespace).


SEE ALSO
       namespace(n), upvar(n)


KEYWORDS
       context, level, namespace, stack frame, variables



Tcl                                                                                               uplevel(n)