Programming Perl, 4th Edition

Interpolating Array Values

Array variables are interpolated into double-quoted strings by joining all elements of the array with the separator specified in the $" variable^[51] (which contains a space by default). The following are equivalent:

my $temp = join( $", @ARGV );
print $temp;

print "@ARGV";

Within search patterns, which also undergo double-quotish interpolation, there is an unfortunate ambiguity: is /$foo[bar]/ to be interpreted as /${foo}[bar]/ (where [bar] is a character class for the regular expression), or as /${foo[bar]}/ (where [bar] is the subscript to array @foo)? If @foo doesn’t otherwise exist, it’s obviously a character class. If @foo exists, Perl takes a good guess about [bar] and is almost always right.^[52] If it does guess wrong, or if you’re just plain paranoid, you can force the correct interpretation with braces as shown earlier. Even if you’re merely prudent, it’s probably not a bad idea.

^[51] $LIST_SEPARATOR if you use the English module bundled with Perl.

^[52] The guesser is too boring to describe in full, but basically takes a weighted average of all the things that look like character classes (a–z, \w, initial ^) versus things that look like expressions (variables or reserved words).