nixCraft

Hi,

I have small dought and got a bit confused about this code.

flags=""
while getopts "difPRrvw" opt
do
case $opt in
f ) exec cp "$@" ;;
* ) flags="$flags - $opt" ;;
esac
done

shift $(( $OPTIND - 1 ))

Actually this code is a part of the script which uses to make a duplicate copy of file/directory when ever there is an usage of cp command..

here flags are nothing but the "options given"

So can anybody help me out to understand these code line by line as i totally couldnt work around it.

What is OPTIND, opt, getopts etcc...?

Let me know your ideas and helps..
Thanks in Advance

Mahesh

Hi,

Again i am having one more line as

exec $cp $flags "$@"
This line is the last line in the script.

in previous post $cp is nothing but /bin/cp
$@ -- for all parameters i understand but why it is been used here
I hope you people will help me out in understanding these things..

Thanks in advance

The getopts command is use by shell to parse command line argument.

Syntax is
getopts {optsring} {variable1}

Where
optstring contains the option letters to be recognized

So in your script difPRrvw all are option to /bin/cp commands. All theses options can be read from man cp command.

$@ means all arguments passed to shell script.
OPTIND is special variable of getopts command which is nothing bit The index of the next argument to be processed by the getopts

Opt is variabe name when option matches it places in varilable opt. This is just variable name it can be anything.

So each time it is getopts get called it places the next option in the shell variable opt, initializing opt if it does not exist, and the index of the next argument to be processed into the variable OPTIND

$@ is used to match what ever source and target directory passed to script are passed as it is to /bin/cp command. So if script called as follows
./script –fir /home/ab/ab1.txt /home/ab/ab2.txt /backup

$@ will match to /home/ab/ab1.txt /home/ab/ab2.txt /backup

while getopts "difPRrvw" opt --> this line will scan all command line args passes to script
do
case $opt in
f ) exec cp "$@" ;; --> when option f encounters it will only run cp command
* ) flags="$flags - $opt" ;; --> This will add all arguments to flags variable
esac
done

shift $(( $OPTIND - 1 )) --> This will shift the index of the next argument

Hope this clears your mind. Feel free to ask more

Also checkout http://nixcraft.net/linux/lsst/ch04sec13.html

Hi Vivek,

Its cool..
Its was very good explanation..
Thanks for your help and sepending some time on it..

Mahesh