Soundex Algorithm in AWK

# Soundex Algorithm in AWK: Michael Sanders 2024
# example usage: awk -f soundex.awk < words.txt
# see also: https://en.wikipedia.org/wiki/Soundex

{ print $0 " : " soundex($0) }

function soundex(word, i, code, c, firstLetter, lastCode, buf) {
  word = toupper(word) # convert word to uppercase
  firstLetter = substr(word, 1, 1)
  code = buf = ""

  # map of letters to soundex digits
  for (i = 2; i <= length(word); i++) {
    c = substr(word, i, 1)
    if (c ~ /[BFPV]/)          code = "1"
    else if (c ~ /[CGJKQSXZ]/) code = "2"
    else if (c ~ /[DT]/)       code = "3"
    else if (c ~ /[L]/)        code = "4"
    else if (c ~ /[MN]/)       code = "5"
    else if (c ~ /[R]/)        code = "6"
    else code = "" # skip A, E, I, O, U, H, W, Y

    # ignore consecutive identical codes
    if (code != lastCode && code != "") {
      buf = buf code
      lastCode = code
    }
  }

  # combine 1st letter with buf, pad with zeros or truncate to 4 characters
  return substr(firstLetter buf "000", 1, 4)
}

# eof

--
:wq
Mike Sanders