On Linux there are mutiple options
The typical used one is touch
touch bar.txt
However you may also use echo if you want to create and write to the file right away
The following command tells to create bar.txt and put foo inside of it
echo foo > bar.txt
You may also use >> which appends to an existing file
The following command puts bar at the end of bar.txt, in a other words, bar will display after foo inside bar.txt
echo bar >> bar.txt