Problem Statement

Idiomatically determine all the lowercase and uppercase letters   (of the Latin [English] alphabet)   being used currently by a computer programming language. The method should find the letters regardless of the hardware architecture that is being used (ASCII, EBCDIC, or other).

Display the set of all: that can be used (allowed) by the computer program, where   letter   is a member of the Latin (English) alphabet:     a ──► z     and     A ──► Z.

You may want to mention what hardware architecture is being used, and if applicable, the operating system.

Let's start with the solution:

# syntax: GAWK -f IDIOMATICALLY_DETERMINE_ALL_THE_LOWERCASE_AND_UPPERCASE_LETTERS.AWK
BEGIN {
    for (i=0; i<=255; i++) {
      c = sprintf("%c",i)
      if (c ~ /[[:lower:]]/) {
        lower_chars = lower_chars c
      }
      if (c ~ /[[:upper:]]/) {
        upper_chars = upper_chars c
      }
    }
    printf("%s\n",ARGV[0])
    printf("lowercase %d: %s\n",length(lower_chars),lower_chars)
    printf("uppercase %d: %s\n",length(upper_chars),upper_chars)
    exit(0)
}