Optional option argument with getopts

Question

while getopts "hd:R:" arg; do   case $arg in     h)       echo "usage"        ;;     d)       dir=$OPTARG       ;;     R)       if [[ $OPTARG =~ ^[0-9]+$ ]];then         level=$OPTARG       else         level=1       fi       ;;     \?)       echo "WRONG" >&2       ;;   esac done 

• level refers to the parameter of -R, dir refers to parameters of -d

• when I input ./count.sh -R 1 -d test/ it works correctly

• when I input ./count.sh -d test/ -R 1 it works correctly

• but I want to have it work when I input ./count.sh -d test/ -R or ./count.sh -R -d test/

This means that I want -R to have a default value and for the sequence of commands to be more flexible.

Answer 1

Wrong. Actually getopts does support optional arguments! From the bash man page:

If  a  required  argument is not found, and getopts is not silent,  a question mark (?) is placed in name, OPTARG is unset, and a diagnostic message is printed.  If getopts is silent, then a colon (:) is placed in name  and OPTARG is set to the option character found. 

When the man page says "silent" it means silent error reporting. To enable it, the first character of optstring needs to be a colon:

while getopts ":hd:R:" arg; do     # ...rest of iverson's loop should work as posted  done 

Since Bash's getopt does not recognize -- to end the options list, it may not work when -R is the last option, followed by some path argument.

P.S.: Traditionally, getopt.c uses two colons (::) to specify an optional argument. However, the version used by Bash doesn't.

Answer 2

getopts doesn't really support this; but it's not hard to write your own replacement.

while true; do     case $1 in       -R) level=1             shift             case $1 in               *[!0-9]* | "") ;;               *) level=$1; shift ;;             esac ;;         # ... Other options ...         -*) echo "$0: Unrecognized option $1" >&2             exit 2;;         *) break ;;     esac done