Re: Example of use of (S) flag

Re: Example of use of (S) flag

[Stephane Chazelas]

2015-12-23 19:25:05 +0100, Sebastian Gniazdowski:
> Hello,
> completion says that (S) is "search substrings in #, %, /
> expressions". Can someone provide example of (S) influence? Thanks
[...]

$ a=ababa
$ echo ${(S)a#b}
aaba
$ echo ${(S)a%b}
abaa

Re: Example of use of (S) flag

[Bart Schaefer]

On Dec 23, 11:25pm, Stephane Chazelas wrote:
} Subject: Re: Example of use of (S) flag
}
} 2015-12-23 19:25:05 +0100, Sebastian Gniazdowski:
} > Hello,
} > completion says that (S) is "search substrings in #, %, /
} > expressions". Can someone provide example of (S) influence? Thanks
} [...]
} 
} $ a=ababa
} $ echo ${(S)a#b}
} aaba
} $ echo ${(S)a%b}
} abaa

Note also that ${(S)var:#pat} is not useful; pat must still match the
entire value of $var (or an element of $var in the array case) for the
element to be matched/removed.

Further note that (MS) is sort of a dumbed-down form of backreferences,
returning something similar to the value of $MATCH in an extendeglob
pattern that uses (#m) (except extendedglob is not needed).  E.g.:

% a=abcba
% echo ${(MS)a#b?}
bc
% echo ${(MS)a%b?}
ba

Here are some examples of the use with ${var/pat/repl}:

torch% echo ${a/b*/x}    
ax
torch% echo ${(S)a/b*/x}
axcba
torch% echo ${(S)a//b*/x}
axcxa

Re: Example of use of (S) flag

[Sebastian Gniazdowski]

On 24 December 2015 at 06:01, Bart Schaefer <schaefer@brasslantern.com> wrote:
> Note also that ${(S)var:#pat} is not useful; pat must still match the
> entire value of $var (or an element of $var in the array case) for the
> element to be matched/removed.

Too bad, my original intention was to do what list=(
"${(@M)list:#(#i)*$~search_pattern*}" ) does but with (S) and compare
performance of the two. Was surprised that this list=(
"${(@SM)list:#(#i)$~search_pattern}" ) doesn't work.

Best regards,
Sebastian Gniazdowski

Re: Example of use of (S) flag

[Philippe Troin]

On Wed, 2015-12-23 at 21:01 -0800, Bart Schaefer wrote:
> Further note that (MS) is sort of a dumbed-down form of backreferences,
> returning something similar to the value of $MATCH in an extendeglob
> pattern that uses (#m) (except extendedglob is not needed).  E.g.:

8< snip >8

> torch% echo ${(S)a/b*/x}
> axcba
> torch% echo ${(S)a//b*/x}
> axcxa

I don't understand why in these two examples the star doesn't match the
rest of the string?  I'd expect:

% echo $a
abcba
% echo ${(S)a/b*/x}
ax
% echo ${(S)a//b*/x}
ax

Since b* should match the entire bcba substring.
What did I miss?

Phil.

Re: Example of use of (S) flag

[Mikael Magnusson]

On Mon, Dec 28, 2015 at 7:23 PM, Philippe Troin <phil@fifi.org> wrote:
> On Wed, 2015-12-23 at 21:01 -0800, Bart Schaefer wrote:
>> Further note that (MS) is sort of a dumbed-down form of backreferences,
>> returning something similar to the value of $MATCH in an extendeglob
>> pattern that uses (#m) (except extendedglob is not needed).  E.g.:
>
> 8< snip >8
>
>> torch% echo ${(S)a/b*/x}
>> axcba
>> torch% echo ${(S)a//b*/x}
>> axcxa
>
> I don't understand why in these two examples the star doesn't match the
> rest of the string?  I'd expect:
>
> % echo $a
> abcba
> % echo ${(S)a/b*/x}
> ax
> % echo ${(S)a//b*/x}
> ax
>
> Since b* should match the entire bcba substring.
> What did I miss?

(S) also enables shortest possible match (like # does and ## doesn't).
% a=abiibybeebz
% echo ${a/b*b/x}
axz
% echo ${(S)a/b*b/x}
axybeebz
% echo ${(S)a//b*b/x}
axyxz
% echo ${a#*b}
iibybeebz
% echo ${a##*b}
z

  S   Search substrings as well as beginnings or ends; with # start
from the beginning and with % start from the end of the string. With
substitution via ${.../...} or ${...//...}, specifies non-greedy
matching, i.e. that the shortest instead of the longest match should
be replaced.

-- 
Mikael Magnusson

Example of use of (S) flag

[Sebastian Gniazdowski]

Hello,
completion says that (S) is "search substrings in #, %, /
expressions". Can someone provide example of (S) influence? Thanks

Best regards,
Sebastian Gniazdowski