Re: Should nextfile in BEGINFILE skip ENDFILE?

[Ed Morton]

> On Nov 15, 2020, at 10:06 PM, arnold@skeeve.com wrote:
> 
> Ed Morton <mortoneccc@comcast.net> wrote:
> 
>> I thought that was just saying that given nextfile exists you could write:
>> 
>>     BEGINFILE {
>>         if ( (getline < FILENAME) < 0 ) {
>>            nextfile
>>         }
>>     }
>> 
>> or similar to test if you can open the current file, I didn't get that 
>> the behavior would automatically change if an error occurred.
>> 
>> I have to say I do wish that wasn't the case and nextfile simply behaved 
>> the same in a BEGINFILE as anywhere else and caused ENDFILE to be 
>> evaluated as it's not clear why skipping ENDFILE would always be 
>> desirable,
> 
> In the case of a bad file, you'll never get to ENDFILE.
> 
>> it's not obvious why puting a nextfile in a BEGINFILE would 
>> be related to handling of errors opening files, and it's easy to handle 
>> errors opening files using a getline without this, e.g. if nextfile 
>> behaved the same in BEGINFILE as everywhere else and I wanted to handle 
>> file opening errors gracefully I could just write this clear, brief, 
>> simple code:
>> 
>>     BEGINFILE {
>>         bad_file = 0
>>         if ( (getline < FILENAME) < 0 ) {
>>            print FILENAME, "is a bad file"
>>            bad_file = 1
>>            nextfile
>>         }
>>     }
>> 
>>     ENDFILE {
>>         if ( !bad_file ) {
>>             do stuff
>>         }
>>     }
> 
> The point is that gawk does this for you. Your code should be
> 
>       BEGINFILE {
>           if (ERRNO) {
>              print FILENAME, "is a bad file"
>              nextfile
>           }
>       }
> 
>       ENDFILE {
>           # guaranteed if we reach here that file was good
>           do stuff
>       }
> 
> This is simpler.  Remember that gawk already knows if a file
> it wants to open is bad or not; it gives you a hook in BEGINFILE
> to deal with that if you want to, by using nextfile. If you don't
> bother to deal with it, it throws a fatal error.
> 
> $ gawk 'BEGINFILE { print "before", FILENAME }' /no/such/file
> before /no/such/file
> gawk: cmd. line:1: fatal: cannot open file `/no/such/file' for reading: No 
> such file or directory
> 
> Arnold

Ok thanks for explaining it.

     Ed