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Unit 5: Strings

// true if $var does not contain alphanumeric characters Notes
$found = ereg(“[^0-9a-zA-Z]”, “123abc”); // false
The ^ character can be used without meaning by placing it in a position other than the start of
the characters enclosed in the brackets. For example, “[0-9^]” matches the characters to 9 and the
^ character. Similarly, the - character can be matched by placing it at the start or the end of the
list; for example, “[-123]” matches the characters -, 1, 2, or 3. The characters ^ and - have different
meanings outside the [] character lists.

Anchors
A regular expression can specify that a pattern occurs at the start or end of a subject string using
anchors. The ^ anchors a pattern to the start, and the $ character anchors a pattern to the end of
a string. For example, the expression: ereg(“^php”, $var) matches strings that start with “php”
but not others. The following code shows the operation of both:
$var = “to be or not to be”;
$match = ereg(‘^to’, $var); // true
$match = ereg(‘be$’, $var); // true
$match = ereg(‘^or’, $var); // false

The following illustrates the difference between the use of ^ as an anchor and the use of ^ in a
character list:
$var = “123467”;
// match strings that start with a digit
$match = ereg(“^[0-9]”, $var); // true

// match strings that contain any character other than a digit
$match = ereg(“[^0-9]”, $var); // false
Both start and end anchors can be used in a single regular expression to match a whole string.
The following example illustrates this:

// Must match “Yes” exactly
$match = ereg(‘^Yes$’, “Yes”); // true

$match = ereg(‘^Yes$’, “Yes sir”); // false
Optional and Repeating Characters
When a character in a regular expression is followed by a ? operator, the pattern matches zero or
one times. In other words, ? marks something that is optional. A character followed by + matches
one or more times. And a character followed by * matches zero or more times. Let’s look at concrete
examples of these powerful operators.

The ? operator allows zero or one occurrence of a character, so the expression:

ereg(“pe?p”, $var)
matches either “pep” or “pp”, but not the string “peep”. The * operator allows zero or many
occurrences of the “o” in the expression:

ereg(“po*p”, $var)
and matches “pp”, “pop”, “poop”, “pooop”, and so on. Finally, the + operator allows one to many
occurrences of “b” in the expression:

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