break - Abort looping command



http://purl.org/tcl/home/man/tcl8.4/TclCmd/break.htm

This command is typically invoked inside the body of a looping command such as '''[for]''' or '''[foreach]''' or '''[while]'''. It returns a TCL_BREAK code, which causes a break exception to occur. The exception causes the current script to be aborted out to the innermost containing loop command, which then aborts its execution and returns normally. Break exceptions are also handled in a few other situations, such as the '''[catch]''' command, Tk event bindings, and the outermost scripts of procedure bodies.

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One surprising use of break is to make sure a [foreach] loop runs exactly once (because we're only interested in the list assignment, not the actual body):
======
 foreach {a b} [list $b $a] break



See also:

   * [catch]
   * [continue]
   * [for]
   * [foreach]
   * [while]

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