bug: minor issues in the `grep` chapter

[dwmkerr]

On zsh systems the history file might be smaller. Replace ~/.bash_history with $HISTFILE

Let's break this down. First, we use the -E flag to tell grep to use Extended Regular Expressions. This allows us to use some clever constructs to search for text.

I know what you want to say, but factually this is wrong. You can use history | grep "[0-9]+ man" to achieve exactly the same effect ('use some clever constructs'). Suggestion: Use the history | grep "\[0-9\]+ man" version first, explain briefly it's a different dialect and then introduce the '-E' switch to get back to familiar territory (history | grep -E "[0-9]+ man").

For familiar uses, grep becomes a

Potential typo. 'users'?