Re: Feature request (@M):# with context matches

[Bart Schaefer <schaefer@brasslantern.com>]

On Jan 30,  1:13pm, Sebastian Gniazdowski wrote:
}
} However, grep -C is not very possible to replace with Zsh code.

I'm a little puzzled about how you think this would work in a
parameter substitution context.  Grep operates on a stream of
input lines, parameter substitution works on values in memory.  Do
you propose to capture the entire input in an array before even
performing the search?

In any case the way you want to do this kind of thing is with array
subscript flags.

 r
     Reverse subscripting: if this flag is given, the EXP is taken as a
     pattern and the result is the first matching array element,
     substring or word (if the parameter is an array, if it is a
     scalar, or if it is a scalar and the `w' flag is given,
     respectively).  The subscript used is the number of the matching
     element, so that pairs of subscripts such as `$foo[(r)??,3]' and
     `$foo[(r)??,(r)f*]' are possible if the parameter is not an
     associative array.

 R
     Like `r', but gives the last match.  For associative arrays, gives
     all possible matches.

 i
     Like `r', but gives the index of the match instead; this may not be
     combined with a second argument.

 I
     Like `i', but gives the index of the last match, or all possible
     matching keys in an associative array.

(The docs have a lot more, I just copied the critical bits.)

So you want something like

    while (( ( hit = $list[(i)*$search_pattern*] ) < $#list ))
    do
	print -r -- $list[hit-3,hit+3]
	shift $hit list
    done

with some appropriate checking that (hit-3) doesn't become negative and
wrap around to the other end of the array, and other foo to manage the
possiblity of overlapping contexts.  Note you don't even need the tilde
in $search_pattern, [(i)...] forces everything into pattern context; if
you do NOT want patterns, you need ${(b)search_pattern} (or in older
zsh ${(q)search_pattern} will usually work).