Final answer:
A reciprocating saw is the tool described, which is like a power version of a keyhole saw and capable of cutting straight lines through a reciprocating motion.
Step-by-step explanation:
A tool that is like a power version of a keyhole saw and can cut straight lines is the reciprocating saw. Reciprocating motion, which is the action of a reciprocating saw, involves converting the rotation of a motor into linear motion—either up and down or back and forth. While a jigsaw might also seem fitting, it is typically used for more intricate cuts rather than straight lines. The other options, such as a miter saw and a circular saw, are also capable of cutting straight lines but function differently from the reciprocating saw.