Learning Perl, 5th Edition

Using Simple Patterns

To match a pattern (regular expression) against the contents of $_, simply put the pattern between a pair of forward slashes (/), like we do here:

$_ = "yabba dabba doo";
if (/abba/) {
  print "It matched!\n";
}

The expression /abba/ looks for that four-letter string in $_; if it finds it, it returns a true value. In this case, it’s found more than once, but that doesn’t make any difference. If it’s found at all, it’s a match; if it’s not in there at all, it fails.

Because the pattern match is generally being used to return a true or false value, it is almost always found in the conditional expression of if or while.

All of the usual backslash escapes that you can put into double-quoted strings are available in patterns, so you could use the pattern /coke\tsprite/ to match the 11 characters of coke, a tab, and sprite.

About Metacharacters

Of course, if patterns matched only simple literal strings, they wouldn’t be very useful. That’s why there are a number of special characters, called metacharacters, that have special meanings in regular expressions.

For example, the dot (.) is a wildcard character—it matches any single character except a newline (which is represented by "\n"). So, the pattern /bet.y/ would match betty. Or it would match betsy, or bet=y, or bet.y, or any other string that has bet, followed by any one character (except a newline), followed by y. It wouldn’t match bety or betsey, though, since those don’t have exactly one character between the t and ...