egrep is provided for backwards compatibility only, grep -e may be better

[goekce]

the-unix-workbench/04-Working-with-Unix.Rmd

Lines 420 to 422 in e928de5

	we should use `grep`'s cousin `egrep`, which just extends `grep`'s capabilities.
	If you're using Ubuntu you should use `grep -P` instead of `egrep` for results
	that are consistent with this chapter.

grep man - description states:

the variant programs egrep and fgrep are the same as grep -E and grep -F, respectively. These variants are deprecated, but are provided for backward compatibility.

It could be better to state grep -E instead of egrep.

Last but not least, thanks for this great resource @seankross !