Bash中$#的用途是什么？

Question

我是Bash脚本的新手,有人可以向我解释$#和$？在以下代码中工作？

#!/bin/bash

ARGS=3         # Script requires 3 arguments.
E_BADARGS=85   # Wrong number of arguments passed to script.

if [ $# -ne "$ARGS" ]
then
  echo "Usage: `basename $0` old-pattern new-pattern filename"
  exit $E_BADARGS
fi

old_pattern=$1
new_pattern=$2

if [ -f "$3" ]
then
    file_name=$3
else
    echo "File \"$3\" does not exist."
    exit $E_BADARGS
fi

exit $? 

Answer 1

从Y分钟学习Bash:

# Builtin variables:
# There are some useful builtin variables, like
echo "Last program's return value: $?"
echo "Script's PID: $$"
echo "Number of arguments passed to script: $#"
echo "All arguments passed to script: $@"
echo "Script's arguments separated into different variables: $1 $2..."

Answer 2

来自https://www.gnu.org/software/bash/manual/html_node/Special-Parameters.html

$# 扩展为十进制的位置参数数量.

$? 扩展到最近执行的前台管道的退出状态.