Show help & version info

Like other commands in Unix-like Operating Systems, "-h/--help" prints help information:

# tcpdump -h
tcpdump version 4.9.2
libpcap version 1.9.0-PRE-GIT (with TPACKET_V3)
LibreSSL 2.8.3
Usage: tcpdump [-aAbdDefhHIJKlLnNOpqStuUvxX#] [ -B size ] [ -c count ]
                [ -C file_size ] [ -E algo:secret ] [ -F file ] [ -G seconds ]
                [ -i interface ] [ -j tstamptype ] [ -M secret ] [ --number ]
                [ -Q in|out|inout ]
                [ -r file ] [ -s snaplen ] [ --time-stamp-precision precision ]
                [ --immediate-mode ] [ -T type ] [ --version ] [ -V file ]
                [ -w file ] [ -W filecount ] [ -y datalinktype ] [ -z postrotate-command ]
                [ -Z user ] [ expression ]

While --version shows tcpdump's version:

# tcpdump --version
tcpdump version 4.9.2
libpcap version 1.9.0-PRE-GIT (with TPACKET_V3)
LibreSSL 2.8.3