Learning Perl, Fourth Edition

Using Simple Patterns

To match a pattern (regular expression) against the contents of $_, put the pattern between a pair of forward slashes (/) as 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 eleven characters of coke, a tab, and sprite.

About Metacharacters

If patterns matched only literal strings, they wouldn’t be very useful. That’s why a number of special characters, called metacharacters , 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. It would also match betsy, bet=y, 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 since those don’t have one character between the t and the y. The dot always matches exactly one character.

If you ...