Watch the CMake variable for change.
variable_watch(<variable name> [<command to execute>])
If the specified variable changes, the message will be printed about the variable being changed. If the command is specified, the command will be executed. The command will receive the following arguments: COMMAND(<variable> <access> <value> <current list file> <stack>)
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© 2000–2011 Insight Software Consortium
Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.7/command/variable_watch.html