Hello. This is another Shell Script related post. This article covers getopts for handling option arguments in shell scripts. In Python, this would be argparse.

getopt vs getopts

There are two ways to handle option arguments in shell scripts: getopt and getopts. getopt is an external command while getopts is a bash built-in command. Since getopt behaves differently between BSD (macOS) and GNU (Linux), it’s better to use getopts for portability. [[1][1]]

Usage

So this article focuses on getopts for handling option arguments. The usage is as follows: [[2][2]]

while getopts abc OPT
do
  case $OPT in
     a) echo "use -a option";;
     b) echo "use -b option";;
     c) echo "use -c option";;
  esac
done

The execution result of the above script is as follows:

./a.sh

./a.sh -a
# use -a option

./a.sh -b
# use -b option

./a.sh -d
#./a.sh: illegal option -- d

To suppress error messages in the above script:

- while getopts abc OPT

+ while getopts :abc OPT

Change to this format and error messages won’t be displayed.

To accept arguments in addition to options, add : after the option character as follows:

while getopts a: OPT
do
  case $OPT in
     a) echo "use -a option and input $OPTARG";;
  esac
done

When executed:

./a.sh -a aaa
# use -a option and input aaa

References

Literature

[1]: https://takuya-1st.hatenablog.jp/entry/2015/12/24/234238
[1]:https://takuya-1st.hatenablog.jp/entry/2015/12/24/234238 [2]: https://www.atmarkit.co.jp/ait/articles/2002/13/news025.html
[2]:https://www.atmarkit.co.jp/ait/articles/2002/13/news025.html