printf 打印多行

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。

参考链接

printf – ‘\n’ 打印多行

printf 'a\nb\nc\n' 可以打印多行。但当字符串以 - 开头，比如 printf '-a\n-b\n--c\n'，就会报错“无效的选项”。

应当写 printf -- '-a\n-b\n--c\n'。