- i (PCRE_CASELESS)
-
If this modifier is set, letters in the pattern match both upper and lower case
letters.
- m (PCRE_MULTILINE)
-
By default, PCRE treats the subject string as consisting of a single "line" of characters
(even if it actually contains several newlines). The "start of line" metacharacter (^) matches only
at the start of the string, while the "end of line" metacharacter ($) matches only at the end of
the string, or before a terminating newline (unless D modifier is set). This is the
same as Perl.
When this modifier is set, the "start of line" and "end of line" constructs match
immediately following or immediately before any newline in the subject string, respectively, as
well as at the very start and end. This is equivalent to Perl's /m modifier. If there are no "\n"
characters in a subject string, or no occurrences of ^ or $ in a pattern, setting this modifier has
no effect.
- s (PCRE_DOTALL)
-
If this modifier is set, a dot metacharater in the pattern matches all characters,
including newlines. Without it, newlines are excluded. This modifier is equivalent to Perl's /s
modifier. A negative class such as [^a] always matches a newline character, independent of the
setting of this modifier.
- x (PCRE_EXTENDED)
-
If this modifier is set, whitespace data characters in the pattern are totally
ignored except when escaped or inside a character class, and characters between an unescaped #
outside a character class and the next newline character, inclusive, are also ignored. This is
equivalent to Perl's /x modifier, and makes it possible to include comments inside complicated
patterns. Note, however, that this applies only to data characters. Whitespace characters may never
appear within special character sequences in a pattern, for example within the sequence (?( which
introduces a conditional subpattern.
- e
-
If this modifier is set,
preg_replace() does normal substitution of backreferences in the replacement string,
evaluates it as PHP code, and uses the result for replacing the search string.
Only preg_replace() uses this
modifier; it is ignored by other PCRE functions.
- A (PCRE_ANCHORED)
-
If this modifier is set, the pattern is forced to be "anchored", that is, it is
constrained to match only at the start of the string which is being searched (the "subject
string"). This effect can also be achieved by appropriate constructs in the pattern itself, which
is the only way to do it in Perl.
- D (PCRE_DOLLAR_ENDONLY)
-
If this modifier is set, a dollar metacharacter in the pattern matches only at the
end of the subject string. Without this modifier, a dollar also matches immediately before the
final character if it is a newline (but not before any other newlines). This modifier is ignored if
m modifier is set. There is no equivalent to this modifier in Perl.
- S
-
When a pattern is going to be used several times, it is worth spending more time
analyzing it in order to speed up the time taken for matching. If this modifier is set, then this
extra analysis is performed. At present, studying a pattern is useful only for non-anchored
patterns that do not have a single fixed starting character.
- U (PCRE_UNGREEDY)
-
This modifier inverts the "greediness" of the quantifiers so that they are not
greedy by default, but become greedy if followed by "?". It is not compatible with Perl. It can
also be set by a (?U) modifier setting within the pattern.
- X (PCRE_EXTRA)
-
This modifier turns on additional functionality of PCRE that is incompatible with
Perl. Any backslash in a pattern that is followed by a letter that has no special meaning causes an
error, thus reserving these combinations for future expansion. By default, as in Perl, a backslash
followed by a letter with no special meaning is treated as a literal. There are at present no other
features controlled by this modifier.
- u (PCRE_UTF8)
-
This modifier turns on additional functionality of PCRE that is incompatible with
Perl. Pattern strings are treated as UTF-8. This modifier is available from PHP 4.1.0 or
greater.
