cat words.txt | tr -s " " "\n"| sort | uniq -c | sort -r | awk '{print $2, $1}'
tr -s "" "\ n": the space is replaced with a line break, that is, in a word file one word per line
sort of word sort
uniq -c count the number of words the same number of words in the word
sort -r positive sequence ordering
awk '{print $ 2, $ 1}' according to the output format, i.e. the number of words in the word finally output to