关于back reference的问题

biary

在研读精华贴的过程中，发现如下内容：

If the group doesn't participate in a match, i.e., it is part of an
alternative not taken or a repetition operator allows zero
repetitions of it, then the back reference makes the whole match
fail. For example, `(one()|two())-and-(three\2|four\3)' matches
`one-and-three' and `two-and-four', but not `one-and-four' or
`two-and-three'. For example, if the pattern matches `one-and-',
then its group 2 matches the empty string and its group 3 doesn't
participate in the match. So, if it then matches `four', then
when it tries to back reference group 3--which it will attempt to
do because `\3' follows the `four'--the match will fail because
group 3 didn't participate in the match.

百思不得其解    ，在Solaris bash环境中测试也未得结果，请大家帮忙解释一下，多谢多谢！
# cat tmp
one-and-three
two-and-four
one-and-four
two-and-three
# grep '\(one\(\)|two\(\)\)-and-\(three\2|four\3\)' tmp
#

waker

grep -E '(one()|two())-and-(three\2|four\3)' tmp

biary

[quote]原帖由 "waker"]grep -E '(one()|two())-and-(three\2|four\3)' tmp[/quote 发表：


这个我也试过了，也是没有任何输出结果，真奇怪！

waker

没有sunbox，在linux下是可以的GNU grep2.5.1

biary

[quote]原帖由 "waker"]没有sunbox，在linux下是可以的GNU grep2.5.1[/quote 发表：


果然，谢谢waker。我再查查solaris的man。另外，one和two后面的（）是什么意思呀？

waker

group 2 matches the empty string