What is the meaning of the “keys %+” in perl?

Question

Short question: What\'s mean the

keys %+

in perl?

I saw it in some source code.

Answer 1

The hash %+ has all the matches from named capture groups in regexes in the current scope. It's explained in perlvar under %LAST_PAREN_MATCH and was added in 5.10.

Similar to @+ , the %+ hash allows access to the named capture buffers, should they exist, in the last successful match in the currently active dynamic scope. [..]

The keys function lists all the keys in the hash.

Answer 2

Whenever you see a groovy-looking variable, look it up in perldoc perlvar.

In this case, %+ is the hash that stores the values corresponding to the named captures of the last regex:

Similar to @+ , the %+ hash allows access to the named capture buffers, should they exist, in the last successful match in the currently active dynamic scope. For example, $+{foo} is equivalent to $1 after the following match:

'foo' =~ /(?<foo>foo)/;

See perldoc perlretut for more details.

Answer 3

These docs are what you want:

perldoc -f keys

perldoc -v %+