outlet - an opening that permits escape or release; he blocked the way out; the canyon had only one issue. exit, way out, issue. opening - a vacant or unobstructed space that is man-made; they left a small opening for the cat at the bottom of the door.
Differences between grep, pgrep, egrep, and fgrep (Linux): grep grep is an acronym that stands for Global Regular Expressions Print. grep is a program which scans a specified file or files line by line, returning lines that contain a pattern. A pattern is an expression that specifies a set of strings by interpreting characters as meta-characters.
$$a|b$$. In this case the $|$ sign means that $a$ divides $b$, or that $\frac ba$ is an integer. $$|x|$$. This use is from the unix terminal where it means that the output of the ls-l command is redirected to the command grep Aug , which shows all files last edited in august. Note that this last one isn't really mathematics but I included it as you mentioned it.