The Line Without It

Match a line that does not contain the word "ERROR" anywhere in it.

Everyone reaches for [^ERROR] first, and it is the most expensive misconception in regex. [^...] is a character CLASS: it matches ONE character that is not E, not R and not O — so it rejects "INFO server started" for the O in INFO, while happily matching the single letter "x" inside a line full of ERRORs. There is no "not this word" operator. What you need is a tempered dot: check at every position that the word does not start here, then consume one character — (?:(?!ERROR).)* — repeated across the whole line, anchored end to end so the check really does cover all of it. Negation in regex is a claim about every position, not about a character.