|To delete a given set of characters
|To concat source set with destination set(destination set comes first; t stands for truncate)
|To replace the source set with the destination set(s stands for squeeze)
|This is the REVERSE card in this game, for eg. If you specify -c with -d to delete a set of characters then it will delete the rest of the characters leaving the source set which we specified (c stands for complement; as in doing reverse of something)
cat file.txt | tr -s '[:lower:]' '[:upper:]'