1 
.TH PCREPATTERN 3 "05 October 2013" "PCRE 8.34" 
.TH PCREPATTERN 3 "08 October 2013" "PCRE 8.34" 
2 
.SH NAME 
.SH NAME 
3 
PCRE  Perlcompatible regular expressions 
PCRE  Perlcompatible regular expressions 
4 
.SH "PCRE REGULAR EXPRESSION DETAILS" 
.SH "PCRE REGULAR EXPRESSION DETAILS" 
359 
sure you supply two digits after the initial zero if the pattern character that 
sure you supply two digits after the initial zero if the pattern character that 
360 
follows is itself an octal digit. 
follows is itself an octal digit. 
361 
.P 
.P 
362 
The handling of a backslash followed by a digit other than 0 is complicated. 
The handling of a backslash followed by a digit other than 0 is complicated, 
363 
Outside a character class, PCRE reads it and any following digits as a decimal 
and Perl has changed in recent releases, causing PCRE also to change. Outside a 
364 
number. If the number is less than 10, or if there have been at least that many 
character class, PCRE reads the digit and any following digits as a decimal 
365 

number. If the number is less than 8, or if there have been at least that many 
366 
previous capturing left parentheses in the expression, the entire sequence is 
previous capturing left parentheses in the expression, the entire sequence is 
367 
taken as a \fIback reference\fP. A description of how this works is given 
taken as a \fIback reference\fP. A description of how this works is given 
368 
.\" HTML <a href="#backreferences"> 
.\" HTML <a href="#backreferences"> 
375 
parenthesized subpatterns. 
parenthesized subpatterns. 
376 
.\" 
.\" 
377 
.P 
.P 
378 
Inside a character class, or if the decimal number is greater than 9 and there 
Inside a character class, or if the decimal number following \e is greater than 
379 
have not been that many capturing subpatterns, PCRE rereads up to three octal 
7 and there have not been that many capturing subpatterns, PCRE handles \e8 and 
380 
digits following the backslash, and uses them to generate a data character. Any 
\e9 as the literal characters "8" and "9", and otherwise rereads up to three 
381 
subsequent digits stand for themselves. The value of the character is 
octal digits following the backslash, using them to generate a data character. 
382 
constrained in the same way as characters specified in hexadecimal. 
Any subsequent digits stand for themselves. The value of the character is 
383 
For example: 
constrained in the same way as characters specified in hexadecimal. For 
384 

example: 
385 
.sp 
.sp 
386 
\e040 is another way of writing an ASCII space 
\e040 is another way of writing an ASCII space 
387 
.\" JOIN 
.\" JOIN 
400 
\e377 might be a back reference, otherwise 
\e377 might be a back reference, otherwise 
401 
the value 255 (decimal) 
the value 255 (decimal) 
402 
.\" JOIN 
.\" JOIN 
403 
\e81 is either a back reference, or a binary zero 
\e81 is either a back reference, or the two 
404 
followed by the two characters "8" and "1" 
characters "8" and "1" 
405 
.sp 
.sp 
406 
Note that octal values of 100 or greater must not be introduced by a leading 
Note that octal values of 100 or greater must not be introduced by a leading 
407 
zero, because no more than three octal digits are ever read. 
zero, because no more than three octal digits are ever read. 
3158 
.rs 
.rs 
3159 
.sp 
.sp 
3160 
.nf 
.nf 
3161 
Last updated: 05 October 2013 
Last updated: 08 October 2013 
3162 
Copyright (c) 19972013 University of Cambridge. 
Copyright (c) 19972013 University of Cambridge. 
3163 
.fi 
.fi 