Turning Modes On and Off for Only Part of The Regular Expression Only supported by PCRE and languages that use it. (? X ) makes escaping letters with a backslash an error if that combination is not a valid regex token.(? q ) makes Tcl interpret the regex as a literal string (minus the (?q) characters).(? e ) makes Tcl interpret the regex as a POSIX ERE.(? b ) makes Tcl interpret the regex as a POSIX BRE.Whether they match or don’t match (at) line breaks depends on (? s ) and (? m ). (? d ) corresponds with UNIX_LINES in Java, which makes the dot, caret, and dollar treat only the newline character \n as a line break, instead of recognizing all line break characters from the Unicode standard.Its use is strongly discouraged because it confuses the meaning of the standard quantifier syntax. So (? U ) a * is lazy and (? U ) a * ? is greedy. (? U ) turns on “ungreedy mode”, which switches the syntax for greedy and lazy quantifiers.Only supported by PCRE and languages that use it such as Delphi, PHP and R. (? n ) turns all unnamed groups into non-capturing groups.(? w ) in Tcl makes the caret and dollar match only at the start and the end of the subject string, and prevents the dot from matching line breaks.(? p ) in Tcl makes the caret and dollar match at the start and the end of each line, and makes the dot match line breaks.In Tcl, (? m ) also prevents the dot from matching line breaks.
In Ruby, (? m ) makes the dot match all characters, without affecting the caret and dollar which always match at the start and end of each line in Ruby. (? m ) for “multi-line mode” makes the caret and dollar match at the start and end of each line in the subject string.In Tcl, (? s ) also makes the caret and dollar match at the start and end of the string only. (? s ) for “single line mode” makes the dot match all characters, including line breaks.(? x x ) turn on free-spacing mode, also in character classes.(? c ) makes the regex case sensitive.(? i ) makes the regex case insensitive.To specify multiple modes, simply put them together as in (? i s m x ). In those situation, you can add the following mode modifiers to the start of the regex. The regex functions in R have ignore.case as their only option, even though the underlying PCRE library has more matching modes than any other discussed in this tutorial. Or, the regex flavor may support matching modes that aren’t exposed as external flags.
The handy String.matches() method in Java does not take a parameter for matching options like pile() does.
Sometimes, the tool or language does not provide the ability to specify matching options. You can find the specifics in the tools and languages section of this website. In an application, you’d toggle the appropriate buttons or checkboxes. In a programming language, you pass them as a flag to the regex constructor or append them to the regex literal. Normally, matching modes are specified outside the regular expression. Specifying Modes Inside The Regular Expression