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Re: {} Questions

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porkchop@invalid.foo (Mike Sanders) writes:

> Ben Bacarisse <ben@bsb.me.uk> wrote:
>
>> porkchop@invalid.foo (Mike Sanders) writes:
>> 
>>> Assuming any awk variant...
>>>
>>> 1. Is this valid? (it works with mawk, gawk, busy box awk)
>>>
>>>    BEGIN { debug = 1 }
>>>
>>>    (debug)  { code_here }
>>>
>>>    (!debug) { code_here }
>>>
>>>    END { ... }
>> 
>> Yes, that's valid.  You don't need the ()s round the expressions.
>
> Thanks Ben.
>
>>> 2. what is the name or accepted term in AWK for unamed functions,
>>> main()?
>> 
>> I don't know what you mean.  Can you give an example?
>> 
>> It occurs to me that maybe you think
>> 
>>   (debug) { code }
>> 
>> is a function?  It's not.  It's just a normal pattern/action AWK pair.
>> An AWK pattern can just be an expression.  That expression is evaluated
>> for every input line and, if true, the corresponding action is executed.
>
> And yet there's still more implied nuance somehow. Let me try to articulate
> my thoughts...
>
> - These types of constructs are 'auto' ran per line of input (assuming
>   its not located within another user-written function) that I get.
>   Perhaps a potential efficiency hit to be aware of.

AWK does not have the usual nested syntax you have probably come to
expect.  In, for example, Algol 68 blocks are made up of statements that
can include procedure declarations that include blocks make up of
statements and so on to whatever level of nest you might want.

AWK's top-level syntax -- a list of function declarations and
pattern/action pairs -- is never nested.  It's the outer syntax of a AWK
program and that's it.  None of it can appear inside any other AWK
construct.

> - There's also the scope of variables to consider... Because any
>   variable's located outside of a user-written function or conversely
>   located within a 'bare naked' construct is global, or at least
>   exposed to the entire script's 'world', so I want be careful here...

I think your "conversely" is misplaced.  And some variables inside a
user-defined functions are also global; the exceptions are names written
as parameters to a function, which I think is what you are saying
below.

>   I'm guessing that any construct that lacks a function signature
>   is globally scoped:
>
>   { im_global = 42 }

This does not "lack a function signature", or at least that's a very odd
way of putting it.  It is, presumably, the action of a pattern/action
pair (with maybe an empty pattern).

>   while those with a function signature (located within parentheses)
>   are locally scoped:
>
>   function private(private_var1) { private_var1 = "foo" }

Yes.  The names listed as parameters in the function declaration are
local to the function and denote local variables.  That's why AWK
programmers have to play tricks like adding extra parameters to get
local variables.

> - And 2 more...
>
>   $ awk '{ v="im_global" }'
>
>   $ awk -f foo -v global=55
>
>   Anything within the above 2 are global as well?

Yes, everything is global except for the names parameters in a function
declaration.

> Just thinking aloud here so, I'll let you long time posters describe
> it more lucidly.

-- 
Ben.

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Thread

{} Questions porkchop@invalid.foo (Mike Sanders) - 2024-08-21 05:35 +0000
  Re: {} Questions Ben Bacarisse <ben@bsb.me.uk> - 2024-08-21 09:06 +0100
    Re: {} Questions porkchop@invalid.foo (Mike Sanders) - 2024-08-21 11:48 +0000
      Re: {} Questions Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-08-21 14:08 +0200
        Re: {} Questions Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-08-21 14:10 +0200
        Re: {} Questions porkchop@invalid.foo (Mike Sanders) - 2024-08-21 18:57 +0000
          Re: {} Questions Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-08-22 00:51 +0200
      Re: {} Questions Ben Bacarisse <ben@bsb.me.uk> - 2024-08-21 16:38 +0100
        Re: {} Questions porkchop@invalid.foo (Mike Sanders) - 2024-08-21 19:01 +0000

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