Something I learned the other day blew my mind even after years of using VI/vim. Because I'd also been using grep for years.
The name 'grep' comes from the vi command
g in ex-mode of vi means 'global', so any
:g command will apply to all the text in the current buffer.
p after 're' means print.
g/re/p actually just means a regular expression should go there (a vim regular expression, which is different fromregex in PHP or even a re string in grep - this is where vim magic modes...