Of course, even in simple strings there can be a large problem: lots of characters
you’ll want to test for are used by regular expression engines with a different
meaning. The square braces around
[0-9] are helpful for
specifying that it’s a set starting with zero and going to nine, but what if
you’re actually searching for square braces?
Fortunately, you can “escape” any character that regular expressions use
for something else by putting a backslash in front of it. An expression that looks for left
square brackets would look like
\[. If you need to
include a backslash, just put a second backslash in front of it, as in
Some characters, particularly whitespace characters, are also just difficult to represent in a string without creating strange formatting. Table C-2 shows how to escape them for convenient matching.
Table C-2. Escapes for whitespace characters
Form feed character
Carriage return character