Short Options
./test.sh -a -b -c charlie -d river lorem ipsum
PARSED_ARGUMENTS is -a -b -c=charlie -d=river -- 'lorem'
ALPHA : 1
BETA : 1
CHARLIE : charlie
DELTA : river
Parameters remaining are: lorem
Long Options
./test.sh --alpha --beta --charlie=charlie --delta=river lorem
PARSED_ARGUMENTS is --alpha --beta --charlie 'charlie'
--delta 'river' -- 'lorem'
ALPHA : 1
BETA : 1
CHARLIE : charlie
DELTA : river
Parameters remaining are: lorem
The bash script is in github.
-a and -b are called switches
because they do not take any parameters while -c and -d to take parameters.
In the script, we first set some default values.
ALPHA=unset
BETA=unset
CHARLIE=unset
DELTA=unset
The usage function will be used to show a user the expected inputs if they specify incorrect parameters.
usage()
{
echo "Usage: k8s-setup [ -a | --alpha ]
[ -b | --beta ]
[ -c | --charlie CHARLIE ]
[ -d | --delta DELTA ] filename(s)"
exit 2
}
We use getopt
to get the parameters a user specifies.
PARSED_ARGUMENTS=$(getopt -a -n k8s-setup -o abc:d: --long alpha,beta,charlie:,delta: -- "$@")
We use a colon (:) to indicate that an argument expects a value e.g --charlie=charlie rather than just --charlie.
We have passed the -a option to getopt so that it accepts the single hyphen form of a switch i.e -charlie as well as --charlie are all accepted. With -n k8s-setup
, k8s-setup is the script name. This is displayed if user input causes an error.
./test.sh --alpha --betas --charlie=charlie --delta river lorem
k8s-setup: unrecognized option '--betas'
Usage: k8s-setup [ -a | --alpha ]
[ -b | --beta ]
[ -c | --charlie CHARLIE ]
[ -d | --delta DELTA ] filename(s)
This is more user friendly than.
./test.sh --alpha --betas --charlie=charlie --delta river lorem
getopt: unrecognized option '--betas'
Usage: k8s-setup [ -a | --alpha ]
[ -b | --beta ]
[ -c | --charlie CHARLIE ]
[ -d | --delta DELTA ] filename(s)
If getopt accepts all inputs, it returns a status code of 0. This is how we catch errors.
VALID_ARGUMENTS=$?
if [ "$VALID_ARGUMENTS" != "0" ]; then
usage
fi
The set command takes any arguments after the options (here “--” signals the end of the options) and assigns them to the positional parameters ($0.. $n)
eval set -- "$PARSED_ARGUMENTS"
while :
do
case "$1" in
-a | --alpha) ALPHA=1 ; shift ;;
-b | --beta) BETA=1 ; shift ;;
-c | --charlie) CHARLIE="$2" ; shift 2 ;;
-d | --delta) DELTA="$2" ; shift 2 ;;
# -- means the end of the arguments; drop this, and break out of the while loop
--) shift; break ;;
# If invalid options were passed, then getopt should have reported an error,
# which we checked as VALID_ARGUMENTS when getopt was called...
*) echo "Unexpected argument: $1 "
usage ;;
esac
done
Now we loop through the $1 variable. Each time we have processed a parameter, we use shift to push the parameter off the stack so that the next parameter is not at position $1. If a parameter has a value we use shift 2
so that both the parameter and its argument are pushed off the stack. -- signifies that there are no more parameters and we break out of the loop. * captures any unexpected input and calls the usage function. Any parameters left on the stack are captured by $@.
References
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