$#和${#@}之间的差异

Question

我查看了下面的代码，发现$#和${#@}都打印了相同的值。谁能告诉我这两者有什么区别吗？

# length.sh

E_NO_ARGS=65

if [ $# -eq 0 ]  # Must have command-line args to demo script.
then
  echo "Please invoke this script with one or more command-line arguments."
  exit $E_NO_ARGS
fi  

var01=abcdEFGH28ij
echo "var01 = ${var01}"
echo "Length of var01 = ${#var01}"
# Now, let's try embedding a space.
var02="abcd EFGH28ij"
echo "var02 = ${var02}"
echo "Length of var02 = ${#var02}"

echo "Number of command-line arguments passed to script = ${#@}"
echo "Number of command-line arguments passed to script = $#"

exit 0

Answer 1

每页手册(3.5.3壳体参数扩展)：

${#parameter} 参数长度替换参数值的字符长度。如果参数是@__，或*，则替换的值是位置参数的数目。如果参数是由*或@订阅的数组名称，则替换的值是数组中的元素数。

因此，${#@}只是一个特例，因为$#是表示位置参数数的常用方法。