你需要使用(( )) for arithmetic表达式，类似于：

#!/usr/bin/env bash

numtop="$(wc -l < Toppings)"

while read -rp "Enter from 1 to  $numtop " topp; do
  if (( topp < 1 || topp > numtop )); then
    echo "Enter from 1 to $numtop"
  else
    echo "Good choice"
    break
  fi
done

编辑：按照@jhnc，给定输入是这样的：a[$(date>/dev/tty)],1（第一个答案严重中断）首先检查输入的值是否是严格的数字。

#!/usr/bin/env bash

##: Test also if Toppings is empty if it is a file
##: or just test the value of $numtop.
numtop="$(wc -l < Toppings)"

while printf 'Enter from 1 to %s ' "$numtop"; do
  read -r topp
  case $topp in
    ('')
      printf 'input is empty\n' >&2
       ;;
    (*[!0123456789]*)
       printf '%s has a non-digit somewhere in it\n' "$topp" >&2
       ;;
    (*)
      if (( topp < 1 || topp > numtop )); then
        printf 'You entered %s\n' "$topp"  >&2
      else
        printf 'You entered %s Good choice!\n' "$topp" &&
        break
      fi
     ;;
  esac
done

• 在[[ ... ]]中使用的<和>不适用于bash中的arithmetic expression，参见help test。它用于测试字符串lexicographical
• 请参阅在线bash手册中的Conditional Constructs，并查找[[ expression ]]，其中指出：When used with [[, the ‘<’ and ‘>’ operators sort lexicographically using the current locale.
• 参见How can I tell whether a variable contains a valid number?。
• numtop=$( cat Toppings | wc -l );是UUOC的一种形式