diff options
Diffstat (limited to 'Doc')
| -rw-r--r-- | Doc/Zsh/expn.yo | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/Doc/Zsh/expn.yo b/Doc/Zsh/expn.yo index 2a0655679..ee554e6c1 100644 --- a/Doc/Zsh/expn.yo +++ b/Doc/Zsh/expn.yo @@ -1246,8 +1246,22 @@ as tt(${)var(param)tt(//)var(pat)tt(/)var(repl)tt(}), only the data for the last match remains available. In the case of global replacements this may still be useful. See the example for the tt(m) flag below. +The numbering of backreferences strictly follows the order of the opening +parentheses from left to right in the pattern string, although sets of +parentheses may be nested. There are special rules for parentheses followed +by `tt(#)' or `tt(##)'. Only the last match of the parenthesis is +remembered: for example, in `tt([[ abab = (#b)([ab])# ]])', only the final +`tt(b)' is stored in tt(match[1]). Thus extra parentheses may be necessary +to match the complete segment: for example, use `tt(X((ab|cd)#)Y)' to match +a whole string of either `tt(ab)' or `tt(cd)' between `tt(X)' and `tt(Y)', +using the value of tt($match[1]) rather than tt($match[2]). + If the match fails none of the parameters is altered, so in some cases it -may be necessary to initialise them beforehand. +may be necessary to initialise them beforehand. If some of the +backreferences fail to match --- which happens if they are in an alternate +branch which fails to match, or if they are followed by tt(#) and matched +zero times --- then the matched string is set to the empty string, and the +start and end indices are set to -1. Pattern matching with backreferences is slightly slower than without. ) |