Pattern Modifiers

The current possible PCRE modifiers are listed below. The names in parentheses refer to internal PCRE names for these modifiers. Spaces and newlines are ignored in modifiers, other characters cause error.

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 metacharacter 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 commentary 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 (PREG_REPLACE_EVAL)

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michal dot kocarek at brainbox dot cz ¶

5 years ago

In case you're wondering, what is the meaning of "S" modifier, this paragraph might be useful:

When "S" modifier is set, PHP calls the pcre_study() function from the PCRE API before executing the regexp. Result from the function is passed directly to pcre_exec().

For more information about pcre_study() and "Studying the pattern" check the PCRE manual on www.pcre.org/pcre.txt

PS: Note that function names "pcre_study" and "pcre_exec" used here refer to PCRE library functions written in C language and not to any PHP functions.