modify or delete variable

modify or delete variable

[Ray Andrews]

[-- Attachment #1: Type: text/plain, Size: 350 bytes --]

     var=( ${(M)var:#*(#i)$substring*} )
     var=( ${var//(#bi)($substring)/aaa${match[1]}bbb )

... can those to operations be combined?  If a string exists in a 
variable, modify it, else delete it?  I'm betting yes.  Mind, there's 
nothing wrong with two easy to understand steps even if a microsecond 
might be saved by combining them.

[-- Attachment #2: Type: text/html, Size: 630 bytes --]

Re: modify or delete variable

[Lawrence Velázquez]

On Sat, Apr 6, 2024, at 10:57 AM, Ray Andrews wrote:
>     var=( ${(M)var:#*(#i)$substring*} )
>     var=( ${var//(#bi)($substring)/aaa${match[1]}bbb )
>
> ... can those to operations be combined?  If a string exists in a 
> variable, modify it, else delete it?

var=(${${(M)var:#*(#i)$substring*}//(#bi)($substring)/aaa${match[1]}bbb})

-- 
vq

Re: modify or delete variable

[Ray Andrews]

On 2024-04-07 01:10, Lawrence Velázquez wrote:
> On Sat, Apr 6, 2024, at 10:57 AM, Ray Andrews wrote:
>>      var=( ${(M)var:#*(#i)$substring*} )
>>      var=( ${var//(#bi)($substring)/aaa${match[1]}bbb} )
>>
>> ... can those to operations be combined?  If a string exists in a
>> variable, modify it, else delete it?
> var=(${${(M)var:#*(#i)$substring*}//(#bi)($substring)/aaa${match[1]}bbb})
>
Yeah, nesting like that would have to work.  It's hard on the eyes at 
first  but the step by step substitution logic is there.  But I wonder 
why this doesn't work:

     var=( ${(M)var//(#bi)($substring)/aaa${match[1]}bbb} )

... seems to me the (M) would have the same function -- if the substring isn't there to be matched it can't be modified so kill the line. In both cases the rule would be that empty lines are removed. Functionality would be added and AFAICT nothing would be lost or broken. The (M) doesn't throw an error but neither does it do anything.  Or ... is this one of those things were it is doing something but I misread the intention?

Re: modify or delete variable

[Bart Schaefer]

On Sun, Apr 7, 2024 at 9:24 AM Ray Andrews <rayandrews@eastlink.ca> wrote:
>
> On 2024-04-07 01:10, Lawrence Velázquez wrote:
> > var=(${${(M)var:#*(#i)$substring*}//(#bi)($substring)/aaa${match[1]}bbb})
> >
> Yeah, nesting like that would have to work.  It's hard on the eyes at
> first  but the step by step substitution logic is there.  But I wonder
> why this doesn't work:
>
>      var=( ${(M)var//(#bi)($substring)/aaa${match[1]}bbb} )

It doesn't work because the (M) flag only applies to the ${...#...} or
${...%...} replacements.  This is documented.

> ... seems to me the (M) would have the same function -- if the substring isn't there to be matched it can't be modified so kill the line.

That doesn't make sense in any case -- (M) means "include the matched
string", that is, reverse the effect of the :# operator which means
"delete the matching value".  What's the "reverse" of "replace A with
B anywhere"?  Certainly not "delete everything".

Re: modify or delete variable

[Ray Andrews]

[-- Attachment #1: Type: text/plain, Size: 500 bytes --]



On 2024-04-07 10:53, Bart Schaefer wrote:
>> ... seems to me the (M) would have the same function -- if the substring isn't there to be matched it can't be modified so kill the line.
> That doesn't make sense in any case -- (M) means "include the matched
> string", that is, reverse the effect of the :# operator which means
> "delete the matching value".  What's the "reverse" of "replace A with
> B anywhere"?  Certainly not "delete everything".
>
Yup, another example of getting the story wrong.

[-- Attachment #2: Type: text/html, Size: 1034 bytes --]