pipeline and redirect

1. almost all the return data is text type.
2. pipeline collect different commands into complicated one.
3. data stream
        1. STDIN -0
        2. STDOUT -1
        3. STDERR -2
4. redirect
        1. >             STDIN->file(override)
        2. >>           STDIN->file(add)
        3. 2>           STDERR->file
        4. 2>&1       STDERR->STDIN
        5. <             file->STDIN
5. pipeline
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