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Diffstat (limited to 'pcre/doc/html/pcrepattern.html')
| -rw-r--r-- | pcre/doc/html/pcrepattern.html | 41 |
1 files changed, 28 insertions, 13 deletions
diff --git a/pcre/doc/html/pcrepattern.html b/pcre/doc/html/pcrepattern.html index 71fd907d26f..55034a7edf6 100644 --- a/pcre/doc/html/pcrepattern.html +++ b/pcre/doc/html/pcrepattern.html @@ -329,7 +329,8 @@ A second use of backslash provides a way of encoding non-printing characters in patterns in a visible manner. There is no restriction on the appearance of non-printing characters, apart from the binary zero that terminates a pattern, but when a pattern is being prepared by text editing, it is often easier to use -one of the following escape sequences than the binary character it represents: +one of the following escape sequences than the binary character it represents. +In an ASCII or Unicode environment, these escapes are as follows: <pre> \a alarm, that is, the BEL character (hex 07) \cx "control-x", where x is any ASCII character @@ -353,19 +354,33 @@ data item (byte or 16-bit value) following \c has a value greater than 127, a compile-time error occurs. This locks out non-ASCII characters in all modes. </P> <P> -The \c facility was designed for use with ASCII characters, but with the -extension to Unicode it is even less useful than it once was. It is, however, -recognized when PCRE is compiled in EBCDIC mode, where data items are always -bytes. In this mode, all values are valid after \c. If the next character is a -lower case letter, it is converted to upper case. Then the 0xc0 bits of the -byte are inverted. Thus \cA becomes hex 01, as in ASCII (A is C1), but because -the EBCDIC letters are disjoint, \cZ becomes hex 29 (Z is E9), and other -characters also generate different values. +When PCRE is compiled in EBCDIC mode, \a, \e, \f, \n, \r, and \t +generate the appropriate EBCDIC code values. The \c escape is processed +as specified for Perl in the <b>perlebcdic</b> document. The only characters +that are allowed after \c are A-Z, a-z, or one of @, [, \, ], ^, _, or ?. Any +other character provokes a compile-time error. The sequence \@ encodes +character code 0; the letters (in either case) encode characters 1-26 (hex 01 +to hex 1A); [, \, ], ^, and _ encode characters 27-31 (hex 1B to hex 1F), and +\? becomes either 255 (hex FF) or 95 (hex 5F). +</P> +<P> +Thus, apart from \?, these escapes generate the same character code values as +they do in an ASCII environment, though the meanings of the values mostly +differ. For example, \G always generates code value 7, which is BEL in ASCII +but DEL in EBCDIC. +</P> +<P> +The sequence \? generates DEL (127, hex 7F) in an ASCII environment, but +because 127 is not a control character in EBCDIC, Perl makes it generate the +APC character. Unfortunately, there are several variants of EBCDIC. In most of +them the APC character has the value 255 (hex FF), but in the one Perl calls +POSIX-BC its value is 95 (hex 5F). If certain other characters have POSIX-BC +values, PCRE makes \? generate 95; otherwise it generates 255. </P> <P> After \0 up to two further octal digits are read. If there are fewer than two -digits, just those that are present are used. Thus the sequence \0\x\07 -specifies two binary zeros followed by a BEL character (code value 7). Make +digits, just those that are present are used. Thus the sequence \0\x\015 +specifies two binary zeros followed by a CR character (code value 13). Make sure you supply two digits after the initial zero if the pattern character that follows is itself an octal digit. </P> @@ -3249,9 +3264,9 @@ Cambridge CB2 3QH, England. </P> <br><a name="SEC30" href="#TOC1">REVISION</a><br> <P> -Last updated: 08 January 2014 +Last updated: 14 June 2015 <br> -Copyright © 1997-2014 University of Cambridge. +Copyright © 1997-2015 University of Cambridge. <br> <p> Return to the <a href="index.html">PCRE index page</a>. |