50.8 Supported PCRE syntax

Since the PCRE syntax is so overwhelming complex, it’s easier to just list what (vicare irregex) does not support for now. Refer to the PCRE documentation for details.¹⁸

• Unicode character classes (\P) are not supported, but will be in an upcoming release. \C named characters are not supported.
• Callbacks, subroutine patterns and recursive patterns are not supported. (*FOO) patterns are not supported and may never be.
• \G and \K are not supported.
• Octal character escapes are not supported because they are ambiguous with back–references; just use hex character escapes.

Other than that, everything should work, including named submatches, zero–width assertions, conditional patterns, etc.

In addition, \< and \> act as beginning–of–word and end–of–word marks, respectively, as in Emacs regular expressions.

Also, two escapes are provided to embed SRE patterns inside PCRE strings, "\'<sre>" and "(*'<sre>)". For example, to match a comma–delimited list of integers we could use:

"\\'integer(,\\'integer)*"

and to match a URL in angle brackets we could use:

"<('*http-url)>"

note in the second example the enclosing "('*...)" syntax is needed because the Scheme reader would consider the closing ‘>’ as part of the SRE symbol.

The following chart gives a quick reference from PCRE form to the SRE equivalent:

;; basic syntax
"^"                     ;; bos (or eos inside (?m: ...))
"$"                     ;; eos (or eos inside (?m: ...))
"."                     ;; nonl
"a?"                    ;; (? a)
"a*"                    ;; (* a)
"a+"                    ;; (+ a)
"a??"                   ;; (?? a)
"a*?"                   ;; (*? a)
"a+?"                   ;; (+? a)
"a{n,m}"                ;; (** n m a)

;; grouping
"(...)"                 ;; (submatch ...)
"(?:...)"               ;; (: ...)
"(?i:...)"              ;; (w/nocase ...)
"(?-i:...)"             ;; (w/case ...)
"(?<name>...)"          ;; (=> <name>...)

;; character classes
"[aeiou]"               ;; ("aeiou")
"[^aeiou]"              ;; (~ "aeiou")
"[a-z]"                 ;; (/ "az") or (/ "a" "z")
"[[:alpha:]]"           ;; alpha

;; assertions
"(?=...)"               ;; (look-ahead ...)
"(?!...)"               ;; (neg-look-ahead ...)
"(?<=...)"              ;; (look-behind ...)
"(?<!...)"              ;; (neg-look-behind ...)
"(?(test)pass|fail)"    ;; (if test pass fail)
"(*COMMIT)"             ;; commit