tr
TextPackage: coreutils
Replaces or deletes characters in a stream: tr -d '\r' strips the Windows line endings that make a script "not found" while it is right there.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
tr -d- Deletes the given characters instead of translating them.
tr -c- Takes the *complement* of the set: everything except the given characters.
Lessons that teach it
No lesson names it among its useful commands; it appears inside other lessons' command lines.