Use grep to find any lines with duplicate words on it.
Use sed to append to the end of everly line a period if not already there.
Use sed to append to the end of everly line a period if some sort of punctuation not already there.
Use sed to substitute the 2nd from last space (ASCII 32) on line with a -.
Use sed to substitute the 3nd from last space (ASCII 32) on line with a -.
Use sed to substitute the 1st space (ASCII 32) on line with a -.
Use sed to substitute the 2nd space (ASCII 32) on line with a -.
Use sed to substitute the 3nd space (ASCII 32) on line with a -.
Use sed to display only lines 7, 14, Use -n option and the p modifier. 
Use sed to display only lines 9, 22, Use -n option and the p modifier. 
Use sed to display only lines beginning with a capital word, Use -n option and the p modifier. 
Use sed to display only lines containing exactly 4 words. Use word anchors.
Use sed to display only lines containing exactly 6 words. Use word anchors.
Use sed to display only lines containing at least 3 words. Use word anchors.
Use sed to display only lines containing at least 5 words. Use word anchors.
Use sed to find a 6 letter word in the line and append a colon and the found word to the end of the line.
Use sed to find a 4 letter word in the line and append a colon and the found word to the end of the line.
Use sed to swap the 1st and second word in the line.
Use sed to swap the last 2 words in the line.
Use sed to replace all spaces in line with a comma.
Use sed to replace all spaces in line with a comma and a space.
Use sed to append a comma to the end of all words, including the last word. Use word anchor.
Use sed to prepend a colon to the start of all words. Use word anchor.