Page 583 - Beginning PHP 5.3

Chapter 18: String Matching with Regular Expressions
So to match a digit character anywhere in the target string you could use either of the following two
expressions:
/[0-9]/
/\d/

Incidentally, you can also use a shorthand character class within a longhand class. The following

expression matches the letter “ e” or “ p ” , or any digit, in the target string:

/[ep\d]/
Here are some examples:

echo preg_match( “/\d[A-Z]/”, “3D” ); // Displays “1”
echo preg_match( “/\d[A-Z]/”, “CD” ); // Displays “0”
echo preg_match( “/\S\S\S/”, “6 & c” ); // Displays “1”
echo preg_match( “/\S\S\S/”, “6 c” ); // Displays “0”

To match any character at all, use a dot ( . ):

echo preg_match( “/He.../”, “Hello” ); // Displays “1”
Matching Multiple Characters

If you want to match the same character (or character class) multiple times in a row, you can use
quantifiers . A quantifier is placed after the character or character class, and indicates how many times that
character or class should repeat in the target string. The quantifiers are:

Quantifier Meaning
* Can occur zero or more times

+ Can occur one or more times
? Can occur exactly once, or not at all
{ n Must occur exactly n times

}
{ n, Must occur at least n times

}
{ n,m Must occur at least n times but no more than m times

}
For example, you can match a string of at least one digit with:
/\d+/

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