Hi all,

I'm bothering you only to ask if this behaviour is what's actually expected (and why, of course): 

#!/usr/bin/perl
use strict;
use warnings;

my @lines = split /\n/, <<'END';
begin{verbatim}
hello all
end{verbatim}
END

s{((?:begin|end))\{verbatim\}}{$1\{whatever\}} for @lines;
print "$_\n" for @lines;

__END__
poletti@Polebian:~/sviluppo/perl/pwc/tmp$ perl bug.pl
Use of uninitialized value in substitution iterator at bug.pl line 11.
Use of uninitialized value in substitution iterator at bug.pl line 11.

hello all

[download]
The fact is that:
$1\{whatever\}

[download]
is being interpreted as $1{whatever}, i.e. the value corresponding to the whatever key in hash $1, instead of the value of $1, followed by the string {whatever}.

This particular behaviour is a consequence of the unlucky usage of the substitution part delimiters, i.e. {} braces. Should we use another one this would not be triggered, i.e. the following works like a charm (note the square brackets instead of braces in the substitution part):

#!/usr/bin/perl
use strict;
use warnings;

my @lines = split /\n/, <<'END';
begin{verbatim}
hello all
end{verbatim}
END

s{((?:begin|end))\{verbatim\}}[$1\{whatever\}] for @lines;
print "$_\n" for @lines;

__END__
poletti@Polebian:~/sviluppo/perl/pwc/tmp$ perl nobug.pl
begin{whatever}
hello all
end{whatever}

[download]
So, it seems that the escape character \ is being used to allow for embedding braces into braces. But this is not needed at all, as we can see from the following: 
#!/usr/bin/perl
use strict;
use warnings;

my @lines = split /\n/, <<'END';
begin{verbatim}
hello all
end{verbatim}
END

my %hash = (whatever => 'world');
s{((?:begin|end))\{verbatim\}}{$hash{whatever}} for @lines;
print "$_\n" for @lines;

__END__
poletti@Polebian:~/sviluppo/perl/pwc/tmp$ perl bug2.pl
world
hello all
world

[download]
Perl is perfectly happy with the unescaped braces inside the substitution part, even when this very part is delimited by braces.

Both 5.8.8 and 5.10.0 show the same behaviour. In my view it seems to be a bug; thoughts?

perl -ple'$_=reverse' <<<ti.xittelop@oivalf

Io ho capito... ma tu che hai detto?

In reply to Bug in substitution operator? by polettix

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