bash - Linux 外壳 : for arg; do

Question

阅读 LTP shell code它使用奇怪的 for 循环语法:

for arg; do
    TCID="${TCID}_$arg"
done

1. 它如何接受参数？我希望它循环遍历 $arg，用 $IFS 分隔，但是当尝试 $arg="aa bb"; 时对于精氨酸；做 echo $arg;完成，它什么都不打印。
2. 这是一个 bashism 吗？

Answer 1

这是一种使用 for 循环处理命令行选项的特殊方式。

相当于:

for arg in "$@"; do
    TCID="${TCID}_$arg"
done

它不特定于 bash。它在 POSIX 中定义:

The for Loop

The for loop shall execute a sequence of commands for each member in a list of items. The for loop requires that the reserved words do and done be used to delimit the sequence of commands.

The format for the for loop is as follows:

for name [ in [word ... ]] do  
   compound-list  
done

First, the list of words following in shall be expanded to generate a list of items. Then, the variable name shall be set to each item, in turn, and the compound-list executed each time. If no items result from the expansion, the compound-list shall not be executed. Omitting:

in word ...

shall be equivalent to:

in "$@"