Go to the first, previous, next, last section, table of contents.
If the syntax bit RE_NO_BK_REF
isn't set, then Regex recognizes
back references. A back reference matches a specified preceding group.
The back reference operator is represented by `\digit'
anywhere after the end of a regular expression's digit-th
group (see section Grouping Operators ((
... )
or \(
... \)
)).
digit must be between `1' and `9'. The matcher assigns numbers 1 through 9 to the first nine groups it encounters. By using one of `\1' through `\9' after the corresponding group's close-group operator, you can match a substring identical to the one that the group does.
Back references match according to the following (in all examples below, `(' represents the open-group, `)' the close-group, `{' the open-interval and `}' the close-interval operator):
RE_DOT_NEWLINE
isn't set) string that is composed of two
identical halves; the `(.*)' matches the first half and the
`\1' matches the second half.
You can use a back reference as an argument to a repetition operator. For example, `(a(b))\2*' matches `a' followed by two or more `b's. Similarly, `(a(b))\2{3}' matches `abbbb'.
If there is no preceding digit-th subexpression, the regular expression is invalid.
Go to the first, previous, next, last section, table of contents.