In Finding the right $<*digit*> capture variable Enlil mentioned $^N which I hadn't seen before. Since looking at it I'm not quite sure when one is more useful than other especially since they appear to have identical functionality. In 5.6.1 I'd use $+ in (?{...}) blocks to work with the value most recently captured by a (...) block. I suppose it might also have uses outside a regex but that appears to be pretty stilted - I'm not sure how it is useful to get the last captured value outside of a regex. Or at least the documentation describes $^N as working rather like I thought that $+ worked. So what is the difference?
For reference:
$+
The text matched by the last bracket of the last successful search pattern. This is useful if you don't know which one of a set of alternative patterns matched. For example:$^N/Version: (.*)|Revision: (.*)/ && ($rev = $+);(Mnemonic: be positive and forward looking.) This variable is read-only and dynamically scoped to the current BLOCK.
The text matched by the used group most-recently closed (i.e. the group with the rightmost closing parenthesis) of the last successful search pattern. (Mnemonic: the (possibly) Nested parenthesis that most recently closed.)
This is primarily used inside "(?{...})" blocks for examining text recently matched. For example, to effectively capture text to a variable (in addition to $1, $2, etc.), replace "(...)" with(?:(...)(?{ $var = $^N }))By setting and then using $var in this way relieves you from having to worry about exactly which numbered set of parentheses they are.
This variable is dynamically scoped to the current BLOCK.
In reply to $+ versus $^N by diotalevi
| For: | Use: | ||
| & | & | ||
| < | < | ||
| > | > | ||
| [ | [ | ||
| ] | ] |