I need something simple like date, but in seconds since 1970 instead of the current date, hours, minutes, and seconds.
date doesn\'t seem t
Since bash 5.0 (released on 7 Jan 2019) you can use the built-in variable EPOCHSECONDS.
$ echo $EPOCHSECONDS
1547624774
There is also EPOCHREALTIME which includes fractions of seconds.
$ echo $EPOCHREALTIME
1547624774.371215
EPOCHREALTIME can be converted to micro-seconds (μs) by removing the decimal point. This might be of interest when using bash's built-in arithmetic (( expression )) which can only handle integers.
$ echo ${EPOCHREALTIME/./}
1547624774371215
In all examples from above the printed time values are equal for better readability. In reality the time values would differ since each command takes a small amount of time to be executed.