Here is a utility method to quickly obtain the MacOS version number (for example 10.11.6):

C_TEXT($0;$cmd;$in;$out;$err) $cmd:="sw_vers -productVersion" LAUNCH EXTERNAL PROCESS($cmd;$in;$out;$err) $0:=Replace string($out;Char(Line feed);"")

If the code snippet above is saved as the UTIL_GetMacOSversion project method it could be used like this:

ALERT(UTIL_GetMacOSversion)

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An alternative command that would provide the same output is:

$cmd:="defaults read loginwindow SystemVersionStampAsString"