Often you will need to see if a string contains a group of characters...

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Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.
public static void main(String[] args) { analyze("I am happy about this"); analyze("I am not happy about this"); analyze("I am not! I am happy");...
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Retire thou then unto a secret place, where no one may be able to see thee or to hinder thee, before the completion of the experiment, whether thou shouldest wish to work by day...
characters and situations, on the external side, completely, and conveyshis impression to his readers with scarcely any diminution of force...
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Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.

For instance, you may need to make sure that a single character or given set of characters is alphanumeric or consists of a digit or digits. For this, you will make use of character classes. You can make use of the built-in character classes or make your own.
The built-in character classes are surrounded by two sets of brackets. Character classes of your own making will be surrounded by a single set of brackets.
Built-in character classes
[[:alpha:]] — Any letter, upper or lower case
[[:digit:]] — Digits (0-9)
[[:space:]] — Matches any whitespace character, including spaces, tabs, newlines, returns, and form feeds
[[:upper:]] — Matches only uppercase letters
[[:lower:]] — Matches only lowercase letters
[[:punct:]] — Matches any punctuation mark
[[:xdigit:]] — Matches possible hexadecimal characters
For example, say you wanted to make sure a letter contained punctuation after
“Dear Sir or Madam” salutation.
ereg(“Madam[[:punct:]]”, $str);
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510
Part V: Appendixes Note that if you use the carat symbol (^) within a character class it has the effect of saying not. So, ereg(“Madam[^[:punct]]”, $str) would match only if Madam is not followed by a punctuation mark.
NOTE
The carat symbol can get confusing because it has two distinct meanings. At the beginning of a regular expression it indicates the start of a string. So the following regular expression will match only a string in which a digit is the first character:
^[[:digit]]
But if the carat is not in the first position in the regular expression, it means
“not.” The following regular expression would match a string that does not contain any digits.
[^[:digit:]]
And to put it all together, the following matches a string that starts with a digit but has a second character that is not a digit.
^[[:digit:]][^[:digit:]]
Self-made character classes
Using brackets, you can construct your own character classes either by using ranges of characters or by mixing characters of your choosing. Here are some typical ranges:
◆ a-z — Any lowercase letter
◆ A-Z — Any uppercase letter
◆ 0-9 — Any digit
Note that these are the ones you will see most frequently, but a range could contain a-m or 0-4 if you wished.
These ranges must be put within brackets to become character classes. So
[a-zA-Z]
is identical to [[:alpha:]].
Self-made classes don’t have to contain a range; they can contain any characters you wish.
[dog0-9]
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Appendix F: Regular Expressions Overview
511
This class will match the letters d, o, or g, or any digit.
$str=”drat”;
if(ereg(“^[dog0-9]”, $str))
{
echo “true”;
}else{
echo “false”;
}
This code will print “true”, because the first character in $str is in the class I’ve defined. If we replaced the d in drat with a b, this code would print “false”.
If you need to include a hyphen within a class, the hyphen must be the final Tip
character before the closing bracket of the class. For example [a-zA-Z-]
Multiple Occurrences
The real fun in regular expressions comes when you deal with multiple occurrences.
This is when the syntax starts getting a little thick. I’ll start by looking at three commonly used special characters.
◆ * (asterisk) — Zero or more of the previous character
◆ + — One or more of the previous character
◆ ? — Zero or one of the previous character
Note that if you want to match any of these characters literally, you will need to escape it with a backslash. So, for example, if you want to match the querystring of a URL, say, http://www.mysqlphpapps.com/index.php?foo=mystring, you could do the following:
\?.*$
The first two characters (\?) match the question mark character (?). Note that it matches the literal question mark because it is escaped with a backslash. If it were not escaped, the question mark would have the meaning given in the previous listing. Then the dot matches any a non-newline character. The asterisk matches zero or more of the pervious character. So the combination .* will match any number of characters until a newline. You will see the .* combination frequently. The dollar
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512
Part V: Appendixes sign is the end of string character. So .*$ matches every non newline character to the end of the string.
You would probably want to use a regular expression like the previous one if you need to make use of the querystring in some other context
$str=”http://domain.com/index.php?foo=mystring&bar=otherstring”;
//see the use of the parenthesized substring
//this will assign the matched portion to $array[1]
if (ereg(“\?(.*)$”, $str, $array) )
{
echo “The querystring is “, $array[1];
}
Now that you have the querystring in the variable $array[1], you do further processing on it.
Before you incorporate this code into your script, note that you don’t have to.
You could use the Apache variable $QUERY_STRING or the PHP HTTP_GET_VARS
array.
Moving on, since the plus sign means one or more of the previous character,
[0-9]+
will match a single digit or multiple digits. In the following statement: if (ereg(“jay[0-9]+”, $str) )
jay1 will test true, but jayg will test false, jay2283092002909303 will test true because it’s still “jay” followed by one or more numbers. Even, jay8393029jay will test true.