Re: awk: switch - case statement (GNU Awk 5.0.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.2.0) - Linux Ubuntu 20.04

[Peter Brooks]

Thank you, that makes sense - though pascal would achieve the same result more 
clearly with:

Case 1,2,3,4,5:
Case 7:

Still, I can see that, if there are scripts that rely on this, they’d break if 
it changed.

Anyway, it was so bizarre that I’ll now remember the breaks! 

Sent from my iPad

> On 27 Jun 2020, at 13:18, david kerns <david.t.kerns@gmail.com> wrote:
> 
> 
> awk works that way because C does.
> C does because it's a glorified 'goto'. consider this:
> 
> switch (i) {
> case 1:
> case 2:
> case 3:
> case 5:
> case 7: p = true; break;
> default: p = false;
> }
> 
> if there was an "auto break" after each case you'd have the code in case 7 
> repeated four more times.
> 
>> On Sat, Jun 27, 2020 at 5:00 AM Peter Brooks <peter.h.m.brooks@gmail.com> 
>> wrote:
>> Thank you - it all works perfectly now.
>> 
>> I wonder why C and awk have such a peculiar default. Is there any use-case
>> where the dropping through makes sense?
>> 
>> I used case statements in Pascal quite a bit, and they worked as I'd
>> expect, and I never considered, for a moment, that it was an odd or
>> sub-optimal arrangement.
>> 
>> I can only think that it was, somehow, easier for the language designers,
>> who didn't have to put an implicit break before each 'case'.
>> 
>> On Sat, 27 Jun 2020 at 11:12, Peter Brooks <peter.h.m.brooks@gmail.com>
>> wrote:
>> 
>> > Thank you, that makes sense. I’ll try i.
>> >
>> > Sent from my iPad
>> >
>> > > On 27 Jun 2020, at 10:18, Manuel Collado <mcollado2011@gmail.com> wrote:
>> > >
>> > > El 27/06/2020 a las 10:35, Peter Brooks escribió:
>> > >> I'm finding myself baffled. I've never used the awk 'switch' statement
>> > >> before, so I may be doing something wrong, but it seems bizarre to me.
>> > >> Here's my test:
>> > >>
>> > >> BEGIN {
>> > >>> fred="hello";
>> > >>> switch (fred){
>> > >>> case "jim": print "Jim";
>> > >>> case "hello": print "Hello";
>> > >>> case "fred" : print "fred";
>> > >>> }
>> > >>> }
>> > >>
>> > >> The output is:
>> > >>
>> > >> $ gawk -f $(pwd)/case.awk </dev/null
>> > >>> Hello
>> > >>> fred
>> > >>
>> > >> I'm completely baffled. I'd expect the output to be only the 'Hello'!
>> > >
>> > > From the gawk manual:
>> > >
>> > > "Control flow in the switch statement works as it does in C. Once a
>> > > match to a given case is made, the case statement bodies execute until a
>> > > break, continue, next, nextfile, or exit is encountered, or the end of
>> > > the switch statement itself."
>> > >
>> > > So you need:
>> > >
>> > > BEGIN {
>> > >   fred="hello";
>> > >   switch (fred){
>> > >     case "jim": print "Jim"; break
>> > >     case "hello": print "Hello"; break
>> > >     case "fred" : print "fred"; break
>> > >   }
>> > > }
>> > >
>> > > --
>> > > Manuel Collado - http://mcollado.z15.es
>> >
>> 
>> 
>> -- 
>> Peter Brooks
>> 
>> Skype:  Fustbariclation
>> Twitter: Fustbariclation
>> Author Page: amazon.com/author/peter_brooks