bash - BASH_REMATCH 在 Bash 5.1 中不是只读的有什么用？

Question

我在 release notes of Bash 5.1 中读到:

p. BASH_REMATCH is no longer readonly.

如 Bash Reference Manual 中所述:

The array variable BASH_REMATCH records which parts of the string matched the pattern. The element of BASH_REMATCH with index 0 contains the portion of the string matching the entire regular expression. Substrings matched by parenthesized subexpressions within the regular expression are saved in the remaining BASH_REMATCH indices. The element of BASH_REMATCH with index n is the portion of the string matching the nth parenthesized subexpression.

是的，访问正则表达式的匹配项非常有用:

$ DESERT=pie-cake_berry_cream-sirup
$ [[ $DESERT =~ _(.*)_ ]] && echo "${BASH_REMATCH[1]}"
berry

但是，我看不出这个消息在 Bash 5.1 中有什么用。也就是说，BASH_REMATCH 不是只读的有什么意义？

Answer 1

在this bug-bash mailing list thread ，bashdb 的维护者(一个 Bash 调试器)解释说 BASH_REMATCH 的值可能会在调试钩子(Hook)内部发生变化，并且由于该变量是只读的，因此可以通过运行最初再次设置它的命令来重置它，这很棘手又脆弱:

Current in bash 5.0 and earlier, the value of BASH_REMATCH might chanted inside a debug hook.

Since BASH_REMATCH is read-only, resetting the value on hook return to the debugged program is a bit tricky and fragile...

[...]

The way that bashdb currently resets BASH_REMATCH is to reissue the command that caused the value to get initially set. That is fragile since this set on exit between stepping from the time BASH_REMATCH was set until the time it is last used. In between variables used in the regular expression may have changed.

[...]

Restoring it is just as tricky. As I hope you see all of this is a bit fragile.

在response , Chet 提出让它不是只读的:

How about we just make it not read-only? The shell will still set it when it does regexp matching.