[2]

2.1

ls | grep 'hw[0-9][0-9]*.html'

2.2

for i in `ls | grep 'hw[0-9][0-9]*.html'`
do
   new=`echo $i | sed 's/html$/txt/'`
   mv $i $new
done

Notice that the following two commands:

ls hw*.html
ls hw[0-9]*.html

don't list exactly all the filenames as required because filename expansion in shell doesn't support full regular expression. E.g., * means any string of characters in the shell as opposed to zero or more repetitions of the previous character in a regular expression.

[3]

3.4

ypcat passwd | head -10 | awk 'BEGIN{FS=":"}
{
print $1
}
END{print "Total Number of Lines Processed: " NR}'


3.5

print out the average length of the words in /usr/dict/words

3.6

#!/bin/sh
awk '{
if ( length($1) == len ) print $1
}' len=$1 /usr/dict/words

3.7

awk 'BEGIN{OFS="\t";
          print "word\t\tindex\tlength\n--------\t------\t-----"
}
$1 ~ /.*'$1'.*/ {
     printf "%s\t",$1
     if ( length($1) < 8) {printf "\t" }
     print index($1, "'$1'"),length($1)
     total += length($1)
     num+=1
}
END{
print "=======\t\t=====","=====\n" num " words\t\ttotal",total
}
' /usr/dict/words