[]和[[]]的区别？

yezhulin1982

[ condition ]与[[ condition ]]有什么具体区别？
在哪一种情况下需要用到第二种。

yunccll

[] 是 test 命令的 builtin 扩展，为了效率。

With version 2.02, Bash introduced the [[ ... ]] extended test command, which performs comparisons in a manner more familiar to programmers from other languages. Note that [[ is a keyword, not a command.Bash sees [[ $a -lt $b ]] as a single element, which returns an exit status.
------  Advanced Bash Shell Scripting Guide

所以： [[]]  里面的and 和or 就可以写成  [[ -f file1 && -e file2 ||  -S file3 ]]
用 [] 的话， 需要写成  [ -f file1  -a -e file2   -o -S file3]  
优先用[[]]  可以避免 一些错误。

waker

精华区有

yezhulin1982

THX all!

biglazybug

版主给个链接呗 我找过很久了 13问12篇没找到

yezhulin1982

原帖由 biglazybug 于 2008-11-13 11:27 发表
版主给个链接呗 我找过很久了 13问12篇没找到

I found it
http://bbs.chinaunix.net/viewthread.php?tid=278896&extra=page%3D6%26filter%3Ddigest

biglazybug

谢谢！

freemeditator

稍微搜索一下本论坛就有了

blackold

man bash