Basically it adds a command to run any command in a new tab of the same terminal window you are currently in.
For example, this:
$ tabdo cd/tmp
would launch a new tab, then navigate to /tmp.
To get this trick, just put this in your ~/.bashrc
tabdo (){/usr/bin/osascript 2>/dev/null <<EOF
activate application "Terminal"
tell application "System Events"
keystroke "t" using {command down}
end tell
tell application "Terminal"
repeat with win in windows
try
if get frontmost of win is true then
do script "$@" in (selected tab of win)
end if
end try
end repeat
end tell
EOF}
Here is a demo video, sorry it goes so fast, YouTube sped it up.