#!/bin/sh
#
echo "cbS by Lewis 5/4/2017"

if [ $# -eq 0 ] ; then
 echo "Usage: cbS filename(s) "
 echo " Will make a numbered backup of the files(s) given."
 echo " Files must be in the current directory."
 exit 255
fi

rc=0                         # return code, default is no error
for fn in $*                 # for each filename given on the command line
do
 if [ ! -f $fn ] ; then      # if not found
  echo "File $fn not found."
  rc=1                       # one or more files were not found
 else
  cnt=1                      # file counter
  loop1=0                    # loop flag
  while [ $loop1 -eq 0 ]
  do
   tmp=bak-$cnt.$fn
   if [ ! -f $tmp ] ; then
     cp $fn $tmp
     echo "File "$tmp" created."
     loop1=1                 # end the inner loop
   else
     let cnt++               # try the next one
   fi
  done
 fi
done

exit $rc                     # exit with return code

It starts with a Usage message as it needs at least one filename to work on.

Note that this command requires the files be in the current directory, so doing something like cbS /tmp/file1.txt will generate an error.

The rc variable is initialized to 0. If a file is not found, it will be set to 1.

Now let's look at the inner loop. The logic here is a backup file will be created from the original file using the cp command. The naming scheme for the backup file is bak-(number).original-filename where number is the next one in sequence. The code determines what the next number is by going through all of the bak-#.filename files until it doesn't find one. That one then becomes the new filename.

Get this one going on your system. Feel free to name it whatever you like, but be careful to name it something other than an existing Linux command. Use the which command to check.

Here is some example output on my system:

This script could be greatly improved upon. It could be made to work with paths/files, and the cp command should be checked for errors. This level of coding will be covered in a later chapter.