Page 579 - Beginning PHP 5.3

Chapter 18: String Matching with Regular Expressions
You can see that, whereas strstr() can match only the exact string passed to it, regular expressions can
contain a series of “ rules ” for creating quite complex matching patterns.

Pattern Matching in PHP

PHP ’ s main pattern - matching function is preg_match() . This function takes the following arguments:

❑ The regular expression to search for (as a string)
❑ The string to search through
❑ An optional array to store any matched text in. (The matched text is stored in the first element.)
❑ An optional integer specifying any flags for the match operation. Currently only one flag is
supported: PREG_OFFSET_CAPTURE . Pass this constant to get preg_match() to return the
position of any match in the array as well as the text matched. (If you need to pass a fifth
argument to preg_match() and you want to turn off this feature, specify a value of zero
instead.)
❑ An optional integer offset from the start of the string (the first character has an offset of zero, the
second character has an offset of 1, and so on). If specified, preg_match() starts the search from
this position in the string, rather than from the first character
preg_match() returns zero if the pattern didn ’ t match, or 1 if it did match. ( preg_match() only finds
the first match within the string. If you need to find all the matches in a string, use preg_match_all() ,
described later in the chapter.)

For example, to match the word “ world ” anywhere in the string “ Hello, world! ” you can write:

echo preg_match( “/world/”, “Hello, world!” ); // Displays “1”
To match “ world ” only at the start of the string, you ’ d write:

echo preg_match( “/^world/”, “Hello, world!” ); // Displays “0”
To access the text that was matched, pass an array variable as the third argument:

echo preg_match( “/world/”, “Hello, world!”, $match ) . “ < br / > ”; //
Displays “1”
echo $match[0] . “ < br / > ”; // Displays “world”

To find out the position of the match, pass PREG_OFFSET_CAPTURE as the fourth argument. The array
then contains a nested array whose first element is the matched text and whose second element is the
position:
echo preg_match( “/world/”, “Hello, world!”,
$match, PREG_OFFSET_CAPTURE ) . “ < br / > ”; // Displays “1”
echo $match[0][0] . “ < br / > ”; // Displays “world”
echo $match[0][1] . “ < br / > ”; // Displays “7”

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