printf '%s\n' $@ 为何可以打印多行?

比如 f() { printf '%s\n' $@; },当执行 f 1 2 3 时会分行打印 1 2 3。

因为根据 POSIX 标准,

The format operand shall be reused as often as necessary to satisfy the argument operands. Any extra b, c, or s conversion specifiers shall be evaluated as if a null string argument were supplied; other extra conversion specifications shall be evaluated as if a zero argument were supplied. If the format operand contains no conversion specifications and argument operands are present, the results are unspecified.

超出 format 字符串的部分,将重复使用 format 字符串。即重复执行 %s\n