gistfile1.sh

#!/bin/env sh

lines=$(tput lines)
cols=$(tput cols)

awkscript='
  {
    letters="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789@#$%^&*()"

    lines=$1
    random_col=$3

    c=$4
    letter=substr(letters,c,1)

    cols[random_col]=0;

    for (col in cols) {
      line=cols[col];
      cols[col]=cols[col]+1;

      printf "\033[%s;%sH\033[2;32m%s", line, col, letter;
      printf "\033[%s;%sH\033[1;37m%s\033[0;0H", cols[col], col, letter;

      if (cols[col] >= lines) {
        cols[col]=0;
      }
    }
  }
'

echo -e "\e[1;40m"
clear

while :; do
  echo $lines $cols $(( $RANDOM % $cols)) $(( $RANDOM % 72 ))
  sleep 0.05
done | awk "$awkscript"

How to adjust size

#!/bin/env sh

lines=$(tput lines)
cols=$(tput cols)

awkscript='
  {
    letters="ァアィイゥウェエォオカガキギクグケゲコゴサコゴサザシジスズセゼソゾタダチヂッツヅテデトドナニヌネノハバパヒビピフブプヘベペホボポマミムメモャヤュユョヨラリルレロヮワヰヱヲンヴヵヶヷヸヹヺ・ーヽヾabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789@#$%^&*()"

    lines=$1
    random_col=$3

    c=$4
    letter=substr(letters,c,1)

    cols[random_col]=0;

    for (col in cols) {
      line=cols[col];
      cols[col]=cols[col]+1;

      printf "\033[%s;%sH\033[2;32m%s", line, col, letter;
      printf "\033[%s;%sH\033[1;37m%s\033[0;0H", cols[col], col, letter;

      if (cols[col] >= lines) {
        cols[col]=0;
      }
    }
  }
'

echo -e "\e[1;40m"
clear

while :; do
  echo $lines $cols $(( $RANDOM % $cols)) $(( $RANDOM % 72 ))
  sleep 0.05
done | awk "$awkscript"