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Project Notes

getopts

Using the getopts utility for parsing options in shell scripts.

Notes

getopts is a POSIX system utility available on most Unix/Linux style distributions.

It helps scripts retrieve options and option-arguments from a list of parameters.

$ ./example.sh -v -p 35
got p: 35
got v: true

Parsing Options

while getopts "p:v" opt
do
  case $opt in
  p)
    # handling option with parameter -p XX
    p=$OPTARG
    ;;
  v)
    # handling option flag -v
    v=true
    ;;
  \?)
    # handling invalid options
    ;;
  esac
done

Handling Boolean Option Flags

Accepting boolean option flags like -v with while getopts "v" ...:

$ ./example.sh
got p:
got v:
$ ./example.sh -v
got p:
got v: true

Handling Options With Parameters

Accepting boolean option flags like -p XX with while getopts "p:" ...:

$ ./example.sh
got p:
got v:
$ ./example.sh -p 42
got p: 42
got v:

Invalid Parameters

getopts will raise an error if parameters that don’t match the options spec are provided e.g.

$ ./example.sh -x
./example.sh: illegal option -- x
(handling an error)

Usage

  ./example.sh -p value # set "p" to value
  ./example.sh -v       # set "v" true
  ./example.sh -h       # this message

Accepting additional parameters

Note: getopts does not remove options from the shell arguments

If unknown argments comes before options, the options parsing fails silently (effectively skipped):

$ ./example.sh bogative -v -p 42
got p:
got v:

If arguments other than those parsed by getopts are required, they should come first and be removed from the args (using shift) before getopts parsing.

$ ./example.sh magic -v -p 42
magic: detected special argument
got p: 42
got v: true

Credits and References

About LCK#240 bash
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This page is a web-friendly rendering of my project notes shared in the LittleCodingKata GitHub repository.

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