Programming Perl, 4th Edition

Wildcard Metasymbols

Three special metasymbols serve as generic wildcards, each of them matching “any” character (for certain values of “any”). These are the dot (“.”), \C, and \X. None of these may be used in their metacharacter sense in a bracketed character class. You can’t use the dot there because it would match (nearly) any character in existence, so it’s something of a universal character class in its own right. If you’re going to include or exclude everything, there’s not much point in having a bracketed character class. The special wildcards \C and \X have special structural meanings that don’t map well to the notion of choosing a single Unicode character, which is the level at which bracketed character classes work.

The dot metacharacter matches any one character other than a newline. (And with the /s modifier, it matches that, too. In which case use \N to match a non-newline.) Like any of the dozen special characters in a pattern, to match a dot literally, you must escape it with a backslash. For example, this checks whether a filename ends with a dot followed by a one-character extension:

if ($pathname =~ /\.(.)\z/s) {
    say "Ends in $1";
}

The first dot, the escaped one, is the literal character, and the second says “match any character”. The \z says to match only at the end of the string, and the /s modifier lets the dot match a newline as well. (Yes, using a newline as a file extension Isn’t Very Nice, but that doesn’t mean it can’t happen.)

The dot metacharacter is most ...