Week Three Tutorial Exercises

1. Given the following program called mycp

   
   # Copy a file -- final version
   numargs=$#
   filelist=
   copylist=
   # Process the arguments, storing all but the last in filelist
   while [ "$#" -gt 1 ]
   do
       filelist="$filelist $1"
       shift
   done
   to="$1"
   # If less than two args, or if more than two args and last arg
   # is not a directory, then issue an error message
   if [ "$numargs" -lt 2 -o "$numargs" -gt 2 -a ! -d "$to" ]
   then
       echo "Usage: mycp filel file2"
       echo " mycp file(s) dir"
       exit 1
   fi
   # Sequence through each file in filelist
   for from in $filelist
   do
       # See if destination file is a directory
       if [ -d "$to" ]
       then
           tofile="$to/'basename $from'"
       else
           tofile="$to"
       fi
       # Add file to copylist if file doesn't already exist
       # or if user says it's okay to overwrite
       if [ -f "$tofile" ]
       then
           echo "$tofile already exists; overwrite (yes/no)? \c"
           read answer
   	if [ "$answer" = yes ]
   	then
   	    copylist="$copylist $from"
   	fi
       else
   	copylist="$copylist $from"
       fi
   done
   # Now do the copy -- first make sure there's something to copy
   if [ -n "$copylist" ]
   then
       cp $copylist $to
   fi
   

   1. Write a program called mymv that does with the mv command what the above program mycp does with the cp program.
   2. Modify the mycp program to prompt for arguments if none are supplied. A typical execution of the modified version should look like this.

      
                $ mycp
                Source filename? voucher
                Destination filename? voucher.sv
                $
      

      Be sure that the program allows one or both files to be specified with filename substitution characters.
   3. Add a -n option to mycp that supresses the normal check for the existence of the destination files. (Kochan and Wood P235)
2. Here are two programs called prog1 and prog2:

   
                 $ cat prog1
                 e1=100
                 export e1
                 e2=200
                 e3=300
                 prog2
                 $ cat prog2
                 echo $e1 $e2 $e3 $e4
                 $
   

   What output would you expect after typing the following:

   
                 $ e2=20 ; export e2
                 $ e4=40 ; prog1
   

   (Kochan and Wood P272)