[quote=perldoc perlop,Regexp Quote-Like Operators]
The "/g" modifier specifies global pattern matching--that is, matching as many times as possible within the string.  How it behaves depends on the context.  In list context, it returns a list of the substrings matched by any capturing parentheses in the regular expression.  If there are no parentheses, it returns a list of all the matched strings, as if there were parentheses around the whole pattern.

In scalar context, each execution of "m//g" finds the next match, returning true if it matches, and false if there is no further match.  The position after the last match can be read or set using the pos() function; see "pos" in perlfunc.   A failed match normally resets the search position to the beginning of the string, but you can avoid that by adding the "/c" modifier (e.g. "m//gc").  Modifying the target string also resets the search position.
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