'''abs''' is one of several extended math commands available in [Tclx].  It makes the [expr] abs function available as a command, and takes expressions as arguments. ([Tcl 8.5] has its own copy that it puts in the ::tcl::mathfunc [namespace].)

If you don't have that, it can easily be emulated:

 proc abs x {expr {abs($x)}}

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[AMG]: In Tcl 8.4.7, `expr {abs(-0.0)}` returns `-0.0`.  In Tcl 8.6b1, it returns `0.0`.

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See also:

   * [Importing expr functions]
   * [tcl::mathfunc]

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