Re: Iterator to parse multiline string with \\n terminator

[Athanasius]

No need for recursion. Just change the anonymous sub as follows (untested):

my $fh_iterator = sub
{
    my $fh    = shift;
    my $line  = $fh->getline();
       $line .= $fh->getline() while $line =~ m{\\$};

    return $line;
}

Update: Here is a tested script which eliminates the Use of uninitialized value warning reported in the post below:

use strict;
use warnings;
use IO::File;

my  $filename = shift @ARGV;
my  $fh       = IO::File->new($filename, 'r');

sub fh_iterator
{
    my $fh   = shift;
    my $line = $fh->getline();

    if (defined $line)
    {
        $line .= $fh->getline() while $line =~ m{\\$};
    }

    return $line;
}

while (my $line = fh_iterator($fh))
{
    print $line;
}

Output:

16:29 >perl 738_SoPW.pl test.file
foo \
bar \
baz
single line

16:29 >

Hope that helps,

[three18ti]

EDIT: Oh, I'm an idiot... for got to change:

    $line .= $fh_iterator while $line =~ m{\\$};

To:

$line .= $fh->getline while $line =~ m{\\$};

However, the code does return the error below on the last line of my test file...

Use of uninitialized value $line in pattern match (m//) at parser3.pl 
+line 17, <GEN0> line 5.

Begin Original Post

Hmm... well, I get a new error at least:/p>

Use of uninitialized value $line in pattern match (m//) at parser3.pl 
+line 17, <GEN0> line 5.

Here's the accompanying code and test file:

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

use IO::File;

use 5.010;

my $filename = shift @ARGV;

my $fh = IO::File->new($filename, 'r');

sub fh_iterator {
    my $fh = shift;

    my $line = $fh->getline;
       $line .= fh_iterator($fh) while $line =~ m{\\$};
}

while (my $line = fh_iterator $fh ) {
    print $line;
}
__END___
test.file
foo \
bar \
baz
single line

[three18ti]

WRT your edit

What do you think about a return instead of an if? e.g.:

sub fh_iterator {
    my $fh   = shift;
    my $line = $fh->getline();
    return $line unless $line;

    $line .= $fh->getline() while $line =~ m{\\$};

    return $line;
}

I don't think there's any functional difference, but one may be more readable than the other...

Thanks for your help!

[tinita]

return $line unless $line;

make that:
return $line unless defined $line;
theoretically the last line could be missing the newline and only contain "0". then $line would be false and ignored with your code.

[Athanasius]

++tinita for highlighting the important difference between testing for definedness and testing for truth (see perlsyn#Truth-and-Falsehood).

But even with the correction I prefer my version. Readability is in the eye of the programmer, but the first high-level programming subject I took at Uni (in Pascal!) emphasised structured programming, and this has remained with me. I prefer a function to have a single exit point (at the end) where possible. In Perl this is not always optimum, so I’ve had to learn to be flexible. But when — as in this case — the structured version is as straightforward as the non-structured one, I prefer the former. YMMV.

As always in Perl, TMTOWTDI.