Like the alias assignment, write your code in a file that can be sourced.

Put your code in a file called bash-fun.sh. When you are ready to test the function definitions, source the file.

. bash-fun.sh

Remember to documentation in your code.

• Set a trap to trap [ctrl]c, this will be used to cancel the backup.
  • Signal to trap is SIGINT or 2.
  • Set the return code to 1
• Declare the variable fname as a local variable inside function.
• If a name is provided as an argument for getname, assign it to the local variable.
• Otherwise, prompt user for a file-name and read result into fname.
  • Use read -p. The read prompt outputs on the stderr rather than std-out and won't cause issues in the vfile function.
• Use an until loop to run grep on the value read in.
  • Test that provided string starts with an alpha character, upper or lower case, or underscore.
  • Any additional characters are either alpha-numeric or underscore.
  • Remember to redirect all output to /dev/null. We only need status of match.
  • If input bad, test for / (path).
    Inform user that paths are not accepted.
    To do this, echo out error message and redirect std-out to stderr.
    echo message 1>&2
    This should prevent the error from being assigned to variable in the calling script.
  • Re-prompt user for a legal file-name.
• Once a legal name provided, return success and echo out the string.
• getname only tests that the name is a legal flame. It does not actually test for the existence of the file.
• When getname is called, assign its output to a variable in the calling environment.

vfile does the following :

• Declares a local variable for holding the retrieved file-name.
• If vfile is called with an argument, pass that argument to getname.
• Otherwise invoke getname with no arguments.
  If getname's return code is 1,
  then quit function.
  Else
  Assign file-name retrieved by getname to the local variable.
  Endif

• Run the following tests on provided file-name and set the appropriate return code.

     If file is a regular file and is readable
     Then
       If file-name is not a symbolic link.
       then
         display the file-name provided.
         return with a code of 0
  
       else
         display the file-name provided.
         return with a code of 1
       
       end-if
  
     else
       return with a code of 2
  
     end-if
  

If invoked with no arguments, then call vfile function with no arguments.

If invoked with arguments, then call vfile with the 1st argument.

Once vfile has validated the filename, copy the file to $HOME/Backup directory. When you copy the file, use the tstamp alias to generate a time stamp, add append the time-stamp as an extension to the file-name.

Put you tstamp definition in the assignment shell script, so it is activated when the script is run.

Backup should be designed to look for a file in the current directory, so Backup should not accept path information in the filename specified.

Backup does the following :

  Call vfile.
    Remember, vfile will call getname and then check for files existence.

  Assign the returned file-name to a local variable. 
  If vfile does not output a file-name, you can still assign the null
      output to the variable. Use the return code to judge success.

  If return code is 0
  then
    copy the file to $HOME/Backup appending the time-stamp generated by 
      tstamp.

  else if return code is 1
    copy the file-name to $HOME/Backup appending the timestamp.
    You can use the Backup alias as a starting point of coding.
    But use the cp -P option. This will copy the symbolic link, not the
      actual file.  See   man cp

  else
    Inform user the file-name was not valid.

  end-if.