# syntax: GAWK -f URL_DECODING.AWK
BEGIN {
    str = "http%3A%2F%2Ffoo%20bar%2F" # "http://foo bar/"
    printf("%s\n",str)
    while (match(str,/%/)) {
      L = substr(str,1,RSTART-1) # chars to left of "%"
      M = substr(str,RSTART+1,2) # 2 chars to right of "%"
      R = substr(str,RSTART+3)   # chars to right of "%xx"
      str = sprintf("%s%c%s",L,hex2dec(M),R)
    }
    printf("%s\n",str)
    exit(0)
}
function hex2dec(s,  num) {
    num = index("0123456789ABCDEF",toupper(substr(s,length(s)))) - 1
    sub(/.$/,"",s)
    return num + (length(s) ? 16*hex2dec(s) : 0)
}