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Related concepts of PHP regular expression substitution:

Preg_replace: perform search and replacement of regular expressions

Mixed preg_replace (mixed pattern, mixed replacement, mixed subject [, int limit])

Preg_replace: allows you to replace a regular expression that matches your definition in a string.

A simple comment removal function:

Preg_replace ('[(/ *) +. + (* /)]','', $val)

This code removes multiline comments that use the format / * comment * / in PHP and CSS. The three parameters are the regular expression, the string to be replaced, and the target string to be replaced (here to do the removal function, so it is a blank string->''). If you want to match secondary rules, you can use $0 for all matches, $1, $2, and so on.

Search subject for a match for the pattern pattern and replace it with replacement. If limit is specified, only limit matches are replaced, and if limit is omitted or its value is-1, all matches are replaced.

Replacement can contain backreferences in the form of / / n or (since PHP 4.0.4) $n, which is preferred. Each such reference will be replaced with text that matches the subpattern in the nth captured parentheses. N can range from 0 to 99, where / / 0 or $0 refers to the text matched by the entire pattern. Count the left parentheses from left to right (starting at 1) to get the number of subpatterns.

When a replacement pattern is followed by a number after a reverse reference (that is, a number immediately after a matching pattern), the familiar / / 1 symbol cannot be used to represent the reverse reference. For example, / / 11 will make it unclear whether preg_replace () wants a / / 1 back reference followed by a number 1 or a / 11 back reference. The solution in this example is to use / ${1} 1. This results in an isolated $1 backreference, while the other 1 is just text.

Related examples of PHP regular expression substitution:

Example 1. A reverse reference followed by the use of a number.

If a match is found, the replaced subject is returned, otherwise the original subject is returned.

Each parameter of preg_replace () (except limit) can be an array. If both pattern and replacement are arrays, they are processed in the order in which their key names appear in the array. This is not necessarily the same numerical order as the index. If you use an index to identify which pattern will be replaced by which replacement, you should sort the array with ksort () before calling preg_replace ().

Example 2. Using indexed arrays in preg_replace ()

If subject is an array, each item in subject is searched and replaced, and an array is returned.

If both pattern and replacement are arrays, preg_replace () takes out the values in turn to search for and replace subject. If there are fewer values in replacement than in pattern, an empty string is used as the remaining replacement value. If pattern is an array and replacement is a string, this string is used as a replacement value for each value in pattern. The other way around makes no sense.

The / e modifier causes preg_replace () to treat the replacement parameter as PHP code (after the appropriate reverse reference has been replaced). Tip: make sure that replacement forms a legitimate PHP code string, otherwise PHP will report syntax parsing errors on lines that contain preg_replace ().

Example 3. Replace several values

This example outputs:

$startDate = 5Compact 27max 1999

Example 4. Use the / e modifier

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