##too too easy
awk 'NR==10 {print $0}' file.txt

## memory limit Exceeded了
col=`awk '{print NF}' file.txt | head -1`; for ((  i=1; i<$col+1; i++ )); do awk -v VAR=$i '{print $VAR}' file.txt | xargs; done

## 哎 抄网上的 todo awk脚本
#fuck
awk '
{
    for (i = 1; i <= NF; i++)  {
        a[NR, i] = $i
    }
}
NF > p { p = NF }
END {
    for (j = 1; j <= p; j++) {
        str = a[1, j]
        for (i = 2; i <= NR; i++){
            str = str " " a[i, j]
        }
        print str
    }
}' file.txt

#grep 正则表达式todo 转义todo,
#easy
grep -Eo  '^\([0-9]{3}\) [0-9]{3}-[0-9]{4}$|^[0-9]{3}-[0-9]{3}-[0-9]{4}$' file.txt

# tr todo,一行一个,然后sort uniq
# easy
tr -cs "[:alpha:]" "\n" < words.txt | sort -r | uniq -c | awk '{print $2,$1}' | sort -nrk 2