对shell的某些细节还不是十分熟悉，借鉴了好多别人的东西
1. Word Frequency
此题很简单，只要能排序就可以
cat words.txt |tr -s " " "
" sort | unique -c | sort -r | awk '{print $2" "$1}'
2.
Valid Phone Numbers
cat file.txt | awk '/^d{3}-d{3}-d{4}$/| /^([0-9]{3}) [0-9]{3}-[0-9]{4}$/'
3.
Transpose File
cat file.txt| awk '{ max_nf = NF
max_nr = NR
for(x=1;x<=max_nf;x++){
vector[x,NR]=$x;
}
}
END{
for(x = 1;x <= max_nf;x++){
for( y = 1;y <= max_nr ; y++){
printf("%s",vector[x,y])
if (y < max_nr)
printf(" ")
}
if (x < max_nf)
printf("
")
}
}
'
4.