为什么不能重置 IFS 变量？

Question

显示当前变量IFS:

echo $IFS |xxd
00000000: 0a  

我想将 IFS 重置为默认值 \t\n。

IFS=$' \t\n'
echo $IFS |xxd
00000000: 0a  

为什么不能重置 IFS 变量？

Answer 1

您正在正确重置 IFS。问题出在您的 echo 上。你应该使用 echo -n "$IFS" | xxd.

看看 man bash（强调我的）：

Word Splitting

The shell scans the results of parameter expansion, command substitution, and arithmetic expansion that did not occur within double quotes for word splitting.

The shell treats each character of IFS as a delimiter, and splits the results of the other expansions into words on these characters. If IFS is unset, or its value is exactly <space><tab><newline>, the default, then sequences of <space>, <tab>, and <newline> at the beginning and end of the results of the previous expansions are ignored, and any sequence of IFS characters not at the beginning or end serves to delimit words. If IFS has a value other than the default, then sequences of the whitespace characters space and tab are ignored at the beginning and end of the word, as long as the whitespace character is in the value of IFS (an IFS whitespace character). Any character in IFS that is not IFS whitespace, along with any adjacent IFS whitespace characters, delimits a field. A sequence of IFS whitespace characters is also treated as a delimiter. If the value of IFS is null, no word splitting occurs.

由于您没有双引号 IFS，它会通过 shell 的分词逻辑。由于 IFS 本身包含 IFS 个字符，因此 shell 会忽略它们。双引号可以防止这种情况。