sort common usage :-f: ignore case. lower–> upper.
-n: sort with numeric value. $ls -s | sort -n #sort by size
-r: reversed order.
-k: sort by a which column and which key.
e.g. $sort -k 2n [filename] #sort 2nd column with numeric order.
This command count word frequency and print top 10.
$cat * | tr -sc A-Za-z '\012' | sort | uniq -c | sort -n | tail
tr translate or delete characters. here compress runs of non-letters into newline
uniq list he uniq lines. with uniq -c can count appers of each line.