How to execute a command when a file changes

Often there is a need to run a bash command when a file changes. E.g. recompile a latex file on save. We can use a programm called entr to do this.

This will run the command "pdflatex main.tex" every time the content of main.tex changes. The -c option clears the screen in between runs. The -r option terminates the programm if it is still running.