What is the batch file command ": ="?

Question

I have the following batch script:

set logFile=%1_%time:~0,2%_%time:~3,2%.log

set logFile=%logFile: =%

Does anyone know what the second line is all about?

Answer 1

It says replace all spaces with nothing. If logfile was "This Is a Test" then after the second line, it would be "ThisIsaTest" (spaces equal nothing)

Answer 2

MultiverseIT described what's going on. For more detail on environment variable substitution, look at the help for the SET command

Set /?

on the command line