This way of handling command line options and arguments is flexible and allows processing of long options (–help) not only single-letter options (-h).
The practical implementation and usage, together with a shell script template, is presented in the Bash scripting article.
For a simpler implementation based on getops see the previous article, Arguments and options for your Bash scripts.
This implementation does not performs option splitting (-hv will be considered error and not processed as -h -v).
Short note about positional parameters
$#is a special variable that contains the number of arguments passed to the script.- Positional parameter N may be referenced as
${N}, or as$NwhenNconsists of a single digit.$0is reserved and expands to the name of the shell or shell script. - Use
"$@"(keep the quotes) to get all passed arguments as separate words.
See Shell Parameters for more information.
The code
#!/bin/bash
declare -i flag_a=0
declare -i flag_b=0
declare arg_b=''
while :; do
case $1 in
-a|--flaga) # a option received
((flag_a++));;
-b|--flagb) # b option received
((flag_b++))
if [[ -z "$2" ]]; then
printf '[%s] needs an argument!\n' "$1"
exit 1
fi
if [[ "$2" == '--' ]]; then
printf '[%s] needs an argument!\n' "$1"
exit 1
fi
arg_b=$2
shift
;;
--) # explicit end of all options, break out of the loop
shift
break
;;
-?*)
printf '[%s] is an invalid option!\n' "$1"
exit 1
;;
*) # this is the default processing case
# there are no more options, break out of the loop
break
esac
shift
done
if ((flag_a > 0)); then
printf 'Received flag [-a]\n'
fi
if ((flag_b > 0)); then
printf 'The argument for [-b] option is %s\n' "$arg_b"
fi
if (($# > 0)); then
printf 'The are %d remaining arguments:\n' "$#"
printf '%s\n' "$@"
fi
When called with -a -b bbb ccc ddd options and arguments string, the previous script will print:
Received flag [-a]
The argument for [-b] option is bbb
The are 2 remaining arguments:
ccc
ddd