使用 tr 命令将 bash shell 脚本中的字母转换为数字

Question

    #!/bin/bash
    P="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    C="012345678910111213141516171819202122232425"

    OUT=`echo $1 | tr $P $C`
    echo $OUT

I would like to translate the alphabets into decimal numbers starting from 0. I tried like the code I mentioned above. But the output is wrong starting from input 'K'. For eg, when I enter DAD, the output is 303, but when the input is KILL, the output is 1800 which is giving me wrong one. K should be translated into 11 but it's taking only 1. My code is not working for the 2 digit decimal numbers.

Answer 1

simple bash solution takes alphabetic input on stdin - prints index of each letter

# fill P array of a-z
P=({a..z})
# fill C map of a-z to index
declare -A C
for((i=0; i < ${#P[*]}; ++i)); do
  C[${P[i]}]=$i
done
# lowercase input
typeset -l line
while IFS= read -r line; do
# print index of each letter in line
  for((i=0; i<${#line}; ++i)); do
    echo -n "${C[${line:i:1}]}"
  done
  echo
done

Answer 2

A function which will output 1 to 26 for letters a to z as well as A to Z

reverse_nth_letter(){  # With thanks, https://stackoverflow.com/a/39066314/1208218
  P=({a..z})
  declare -A C
  for((i=0;i<${#P[*]};++i)){ C[${P[i]}]=$i; }
  LETTER="$(echo "${1}" | tr '[:upper:]' '[:lower:]')"
  echo -n "$[ ${C[${LETTER}]} + 1 ]"
}