Zsh - Notes
26 Jul 2019command substitution
http://zsh.sourceforge.net/Intro/intro_7.html
Command substitution in zsh can take two forms. In the traditional form, a command enclosed in backquotes (
...
) is replaced on the command line with its output. This is the form used by the older shells. Newer shells (like zsh) also provide another form, $(…). This form is much easier to nest.