osx man page for incr

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

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NAME
       incr - Increment the value of a variable

SYNOPSIS
       incr varName ?increment?
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DESCRIPTION
       Increments the value stored in the variable whose name is varName.  The value of the variable must be an integer.  If increment is supplied
       then its value (which must be an integer) is added to the value of variable varName;  otherwise 1 is added to varName.  The  new  value	is
       stored as a decimal string in variable varName and also returned as result.

       Starting  with  the Tcl 8.5 release, the variable varName passed to incr may be unset, and in that case, it will be set to the value incre- |
       ment or to the default increment value of 1.

EXAMPLES
       Add one to the contents of the variable x:
	      incr x

       Add 42 to the contents of the variable x:
	      incr x 42

       Add the contents of the variable y to the contents of the variable x:
	      incr x $y

       Add nothing at all to the variable x (often useful for checking whether an argument to a procedure is actually integral and  generating	an
       error if it is not):
	      incr x 0

SEE ALSO
       expr(n)

KEYWORDS
       add, increment, variable, value

Tcl																	   incr(n)