Linux：i can not understand a m4 command : My work is converting Linux command into CMake execute_process(COMMAND ...), and there are some differences between them, so i need to understand each Linux command. But this m4 command really  beat me. The m4 command as below:

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    m4 -Isource/analyzer/ -P < source/analyzer/aParser.m4y > source/analyzer/aParser.by

What does this command mean?
