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Re: Why is the error thrown from close(FH) when the error is the missing <> on while(FH)? ( line number mismatch, look above, look before )(Bareword found in conditional)

by Anonymous Monk
on Feb 01, 2013 at 09:03 UTC ( #1016478=note: print w/ replies, xml ) Need Help??


in reply to Why is the error thrown from close(FH) when the error is the missing <> on while(FH)?

My question is: Why is the error not thrown from the while on 83?

It is, it just doesn't say line 83, the line number is wrong, it is a mismatch, example

$ cat junk while( STDIN ){ @ARGV=2; } # 4 # 5 $ perl -w -Mstrict junk Bareword "STDIN" not allowed while "strict subs" in use at junk line 5 +. Execution of junk aborted due to compilation errors.

$ cat junk while( STDIN ){ @ARGV=2; }

I vaguely remember when I first learned to always look at the earliest error message, start at the reported line number, and look before, look above -- this is especially true in perl :)

But you've found a new bug in strict.pm, consider

$ cat junk while( STDIN ){ @ARGV=2; } close STDIN;

With strict the following error message is misleading

$ perl -Mstrict junk Bareword "STDIN" not allowed while "strict subs" in use at junk line 4 +. Execution of junk aborted due to compilation errors.

If you look at line 4, you'll see  close STDIN , but we know close takes barewords -- it can be very confusing even if you know to look above

But with warnings the error message is more informative

$ perl -w junk Bareword found in conditional at junk line 4. Terminating on signal SIGINT(2)

Sure, the line number is wrong (and the program runs forever, infinite loop is infinite), but we know  close STDIN; is not a conditional , so there is less confusion

OTOH :) here is where the advantage falls apart , a conditional  close STDIN if fileno STDIN; or  fileno STDIN and close STDIN;

so warnings can detect a bareword in a conditional, strict can name the bareword, strict should say it is in a conditional, its more informative

On the history of the line number bug
Warning gets the line number wrong?
Error messages point to wrong line number in if-elsif construct,
if-elsif weirdness,
No Pause on Elsif in Debugger
https://rt.perl.org/rt3//Public/Search/Simple.html?q=perl5+line+number
#1031: Incorrect line number reporting due to overoptimization
#1034: error line number reported wrong when using here documents
#7084: "Use of uninitialized value" reported on incorrect line number
#8051: -B wrong line number after die
#47632: Undef loop while condition, loop code motion, and bad warning line number? 5.10-RC1 + 5.8.8
#70910: wrong line number in syntax error message
#114070: here-docs cause bogus line numbers
#115768: wrong line number in error message

:) Perl gets the line number right in the beginning (: (see "junk:" below)

$ cat junk while( STDIN ){ @ARGV=@ARGV; } close STDIN ; $ perl -MO=Concise junk h <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 2 <;> nextstate(main 3 junk:1) v:{ ->3 d <2> leaveloop vK/2 ->e 3 <{> enterloop(next->c last->d redo->4) v ->4 - <@> lineseq vK ->d 4 <;> nextstate(main 1 junk:2) v ->5 b <2> aassign[t6] vKS/COMMON ->c - <1> ex-list lK ->8 5 <0> pushmark s ->6 7 <1> rv2av[t5] lK/1 ->8 6 <#> gv[*ARGV] s ->7 - <1> ex-list lK ->b 8 <0> pushmark s ->9 a <1> rv2av[t3] lKRM*/1 ->b 9 <#> gv[*ARGV] s ->a c <0> unstack v ->4 e <;> nextstate(main 3 junk:4) v:{ ->f g <1> close vK/1 ->h f <#> gv[*STDIN] s ->g junk syntax OK

update: :) I acknowledge kcott beat me to the punch , I mean he struck first, I mean I'm not a violent person at all, its just an expression, he posted first :p


Comment on Re: Why is the error thrown from close(FH) when the error is the missing <> on while(FH)? ( line number mismatch, look above, look before )(Bareword found in conditional)
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Re^2: Why is the error thrown from close(FH) when the error is the missing <> on while(FH)? ( line number mismatch, look above, look before )(Bareword found in conditional)
by techgrrl (Acolyte) on Feb 01, 2013 at 16:44 UTC

    Those are some great links! The first one has some good examples of this occurring in other contexts. I have a lot of reading to do.

    Thanks for taking the time to include those references!

    TechGrrl

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