UNIX for Dummies Questions & Answers

Hi,
I am a dummy and hear to the computation guys telling me,
"Oh! that is easy, you just write a wrapper to do all that bunch of stuff!"

Could someone tell me what is a wrapper? The only one I know is Cling-Wrap for sandwiches.

A small elegant example would be very appealing.
Thanks
~GH

You use wrappers when you want to enhance the functionality of an existing utility/command without changing it (usually for backwards compatibility or because you don't have access to the original source code).

An alias is the simplest form of wrapper. You can create the following alias to always get a long listing from the output of ls:

Code:

alias ls='ls -l'

A more complex example could be, lets say, you have a command which processes some sort of message passed as a command line argument:

Code:

process_msg "this is a message"

Now, you want a functionality to pass a file with bunch of messages to be processed. You can write a wrapper which utilizes the existing process_msg utility to process multiple messages:

Code:

function process_file
{
  file=$1
  cat $file | while read msg
  do
    process_msg "$msg"
  done
}
process_file input.dat

Hope that explains!