シェルスクリプトでの大文字と小文字を区別しない真偽の判定処理

yes_or_no.sh

#!/bin/sh

yes_or_no()
{
  case `echo "$1" | tr A-Z a-z` in
    "y"|"yes"|"on"|"true")
      echo "'$1' is YES!!!"
      ;;
    "n"|"no"|"off"|"false")
      echo "'$1' is NO!!!"
      ;;
    *)
      echo "Unknown argument."
      ;;
  esac
}

yes_or_no "y"    # 'y' is YES!!!
yes_or_no "Y"    # 'Y' is YES!!!
yes_or_no "Yes"  # 'Yes' is YES!!!
yes_or_no "NO"   # 'NO' is NO!!!
yes_or_no "tRUe" # 'tRUe' is YES!!!
yes_or_no true   # 'true' is YES!!!
yes_or_no false  # 'false' is NO!!!