1、按单词出现频率降序排序！
2、按字母出现频率降序排序！
the squid project provides a number of resources toassist users design,implement and support squid installations. Please browsethe documentation and support sections for more infomation

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grep -o "[a-Z]" oldboy.log|sort|uniq -c|sort -rn|head -5

sed -r 's#[ .,]##g' oldboy.log|awk -F "" '{for(i=1;i<=NF;i++)S[$i]++}END{for(k in S)print S[k],k}'|sort -rn|head -5