使用负前瞻错误返回 2 的 Bash 双括号正则表达式比较 [英] Bash double bracket regex comparison using negative lookahead error return 2

问题描述

在 Bash 4.1 机器上，

On Bash 4.1 machine,

我正在尝试使用双括号"[[表达式]]使用NEGATIVE LOOKAHEAD"进行正则表达式比较.

I'm trying to use "double bracket" [[ expression ]] to do REGEX comparison using "NEGATIVE LOOKAHEAD".

我做了 "set +H" 来禁用 BASH 变量'!' 扩展到命令历史搜索.

I did "set +H" to disable BASH variable'!' expansion to command history search.

我想匹配任何字符串"，除了arm-trusted-firmware".

set +H
if [[ alsa  =~ ^(?!arm-trusted-firmware).* ]]; then echo MATCH; else echo "NOT MATCH"; fi

我希望这会打印出MATCH"，但它打印不匹配".

I expect this to print "MATCH" back, but it prints "NOT MATCH".

查看双括号"的返回码后，它返回2":

After looking into the return code of "double bracket", it returns "2":

set +H
[[ alsa  =~ ^(?!arm-trusted-firmware).* ]]
echo $?

根据bash手册，返回值 '2' 表示正则表达式在语法上不正确":

According to bash manual, the return value '2' means "the regular expression is syntactically incorrect":

一个额外的二元运算符，=~，可用，具有与 == 和 != 相同的优先级.
使用时，运算符右侧的字符串被视为扩展的正则表达式并相应地匹配(如 regex(3)).
如果字符串与模式匹配，则返回值为 0，否则为 1.如果正则表达式在语法上不正确，条件表达式的返回值为 2.

An additional binary operator, =~, is available, with the same precedence as == and !=.
When it is used, the string to the right of the operator is considered an extended regular expression and matched accordingly (as in regex(3)).
The return value is 0 if the string matches the pattern, and 1 otherwise. If the regular expression is syntactically incorrect, the conditional expression's return value is 2.

我做错了什么?

在我的原始脚本中，我正在与 STRING 列表进行比较.

In my original script, I'm comparing against to a list of STRINGs.

当它匹配时，我触发一些函数调用；

When it matches, I trigger some function calls;

当它不匹配时，我会跳过我的操作.

when it doesn't match, I skip my actions.

所以，是的，从这个例子来看，

So, YES, from this example,

我正在比较alsa"和arm-trusted-firmware"之间的字符串.

I'm comparing literally the STRING between 'alsa' and 'arm-trusted-firmware'.

推荐答案

默认情况下 bash POSIX 标准不支持 PCRE.(来源:Wiki Bash 黑客)

By default bash POSIX standard doesn't supports PCRE. (source: Wiki Bash Hackers)

作为解决方法，您需要启用 extglob.这将启用一些扩展的全局模式:

As workaround, you'll need to enable extglob. This will enable some extended globing patterns:

$ shopt -s extglob

查看 Wooledge Wiki 以了解有关 extglob 的更多信息.

Check Wooledge Wiki for reading more about extglob.

然后你就可以使用这样的模式了:

Then you'll be able to use patterns like that:

?(pattern-list)   Matches zero or one occurrence of the given patterns
*(pattern-list)   Matches zero or more occurrences of the given patterns
+(pattern-list)   Matches one or more occurrences of the given patterns
@(pattern-list)   Matches one of the given patterns
!(pattern-list)   Matches anything except one of the given patterns

在 Wiki Bash Hackers 和 LinuxJournal.

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