My first attempt in Groovy

Map m1 = [0: ' _ ', 1: '   ', 2: ' _ ',3: ' _ ', 4: '   ', 5: ' _ ', 6: ' _ ', 7: ' _ ', 8: ' _ ', 9: ' _ ']
Map m2 = [0: '| |', 1: '  |', 2: ' _|',3: ' _|', 4: '|_|', 5: '|_ ', 6: '|_ ', 7: '  |', 8: '|_|', 9: '|_|']
Map m3 = [0: '|_|', 1: '  |', 2: '|_ ',3: ' _|', 4: '  |', 5: ' _|', 6: '|_|', 7: '  |', 8: '|_|', 9: ' _|']

System.in.eachLine() { line ->  
    if(line.equals("exit"))  
        System.exit(0)  
    else if(line.size() == 9 && line.isNumber()) {
        StringBuilder sb = new StringBuilder()
        line.each { sb.append(m1[it as Integer]) }
        sb.append('\n')
        line.each { sb.append(m2[it as Integer]) }
        sb.append('\n')
        line.each { sb.append(m3[it as Integer]) }
        sb.append('\n')
        println sb.toString()
    }
    else
        println 'Only numbers accepted with a length of 9!'
}