I am taking a course on Lynda and they show this code below. I didn't fully understand some parts. Please see the questions within the code.
Thank you for your input and time.
Regards,
Code:
function usage {
echo Options are -r -h -b -x --branch --version --help --exclude
exit 1
}
function handleopts {
OPTS=`getopt -o r:hb::x: -l exclude: -l branch:: -l help -l version -- "$@"`
#### Question 1: How does the "-- $@" work here ####
if [ $? != 0 ]
then
echo ERROR parsing arguments >&2
exit 1
fi
eval set -- "$OPTS"
#### Question 2: I understand that set -- $variable sets the content of $variable to the positional parameters, but how does it work here? What are the PP here? ####
while true ; do
case "$1" in
-r ) rightway=$2
shift 2;;
#### Question 3: I assume that shift 2 means shift shift, but why is it needed here? ####
--version ) echo "Version 1.2";
exit 0;;
-h | --help ) usage;
shift;;
-b | --branch)
case "$2" in
"") branchname="default" ; shift 2 ;;
*) branchname="$2" ; shift 2 ;;
esac ;;
--) shift; break;;
esac
done
if [ "$#" -ne 0 ]
then
echo Error extra command line arguments "$@"
usage
fi
}
rightway=no
handleopts $@
echo rightway = $rightway
echo branchname = $branchname
Last edited by rbatte1; 02-01-2017 at 09:16 AM..
Reason: Spelling corrections
-- "$@" just means, "take the following arguments literally" and "all the following arguments, properly separated and quoted". If your arguments are "a b" "c d" "e f", "$@" will put them in as "a b" "c d" "e f", not "a" "b" "c" "d" "e" "f".
The 'shift' eats a commandline argument, i.e. converts $1=a, $2=b, $3=c, $4=d into $1=b, $2=c, $3=d. shift 2 moves it all the way to $1=c, $2=d. It's done since that particular branch uses an argument, so it has to remove two things from the list (the -r and the argument following it) not just one.
I have no idea why they're doing 'eval set', only theories. That's dangerous and dumb. They may be trying to process quotes inside quotes.
They are getting the values from 'getopt', the standard way to handle commandline arguments. I can't really explain its workings, but I'm sure others can.
Last edited by Corona688; 02-01-2017 at 11:48 AM..
-- "$@" just means, "take the following arguments literally" and "all the following arguments, properly separated and quoted". If your arguments are "a b" "c d" "e f", "$@" will put them in as "a b" "c d" "e f", not "a" "b" "c" "d" "e" "f".
The 'shift' eats a commandline argument, i.e. converts $1=a, $2=b, $3=c, $4=d into $1=b, $2=c, $3=d. shift 2 moves it all the way to $1=c, $2=d. It's done since that particular branch uses an argument, so it has to remove two things from the list (the -r and the argument following it) not just one.
I have no idea why they're doing 'eval set', only theories. That's dangerous and dumb. They may be trying to process quotes inside quotes.
They are getting the values from 'getopt', the standard way to handle commandline arguments. I can't really explain its workings, but I'm sure others can.
Hi Corona688,
I agree wholeheartedly with your 1st three paragraphs.
But the "standard" way of handing command line arguments is getopts; not getopt. In the early days of the Bourne shell, there was a getopt utility that had problems dealing with quoted option-arguments and was replaced by the getopts utility that is in the current standards. The getopts utility is processed in a loop extracting one option and its option-argument (if there is one for that option) each time through the loop. The version in the standard doesn't have any provision for processing long options (i.e., --optionname or --optionname=argument), but many implementations of the getopts utility have extensions supporting them.
The standard getopts utility can handle command lines like:
producing identical results for any of the above. And, if operand1's 1st character is not a <hyphen>, will also recognize the following producing identical results to any of the above:
One might guess that the getopt utility called by the script in post #1 in this thread would normalize command line arguments splitting multiple option letters following a single <hyphen> into separate arguments each with its own <hyphen> and would split an an option with an option-argument presented as a single argument into two arguments so that the while loop in that script would work properly, but I have no idea whether the getopt actually being used by this application is this flexible.
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