A Groovy script to display given time in different timezones

datetime.groovy

#!/usr/bin/env groovy

//TimeZone.setDefault(TimeZone.getTimeZone('Europe/Warsaw'))

if (args.size() == 0 || !args.find { it ==~ /^\d{2}\.\d{2}\.\d{4}\ \d{2}\:\d{2}$/ }) {
    String thisScript = new File(this.getClass().protectionDomain.codeSource.location.path).getName()
    System.err.println "Error parsing command line arguments!"
    System.err.println "Usage: ${thisScript} <dateTime>"
    System.err.println "Accepted dateTime format is dd.mm.yyyy hh:mm"
    System.err.println "Example: ${thisScript} '25.05.2018 05:00'"
    System.exit(1)
}
else {
    String inputDateTime = args[0]

    // https://docs.oracle.com/javase/8/docs/api/java/text/SimpleDateFormat.html
    String inputDateTimeFormat = 'dd.MM.yyyy HH:mm'
    String outputDateTimeFormat = 'EEEE, d MMMM yyyy, HH:mm z'

    Date dateTime = Date.parse(inputDateTimeFormat, inputDateTime)

    println dateTime.format(outputDateTimeFormat, TimeZone.getTimeZone('America/Los_Angeles'))
    println dateTime.format(outputDateTimeFormat, TimeZone.getTimeZone('America/Chicago'))
    println dateTime.format(outputDateTimeFormat, TimeZone.getTimeZone('Europe/Warsaw'))
    println dateTime.format(outputDateTimeFormat, TimeZone.getTimeZone('Europe/Moscow'))
    println dateTime.format(outputDateTimeFormat, TimeZone.getTimeZone('Asia/Kolkata'))
}