breaking up a file by delimiter

[navalned]

I have the following code that seems to work thus far. However, it just feels like there is a better way to do it. If so I'd love to see it.

use strict;
use warnings;

use Data::Dumper;
$Data::Dumper::Indent = 0;

my $file = "test";
my @data;

{
    local $/ = undef;
    open FILE, "$file" or die $!;

    while (my $line = <FILE>) {
        push @data, split /XXX/, $line; 
        # I thought it should be /^XXX$/, but that didn't work
    }
}

@data = grep /\S/, @data; # I don't understand why I had to do this

print Dumper \@data;

This gives the following correct output:

$VAR1 = ['This is a test.','This is a multiline test.']

The file looks like so:

This is a test.
XXX
This is a multiline
test.
XXX

2018-10-07 Athanasius put code tags around script output and file contents

[hippo]

This gives the following correct output:

$VAR1 = ['This is a test.','This is a multiline test.']

Not on my perl. Here it gives:

$VAR1 = ['This is a test.
','
This is a multiline
test.
'];

As it's hard to know from that what you actually want, here's an SSCCE which preserves the multi-line nature of the second string but removes the trailling newlines. You can amend it to suit your actual requirements.

use strict;
use warnings;

use Test::More tests => 1;

my @data;
my @want = ('This is a test.', "This is a multiline\ntest.");

{
    local $/ = "\nXXX\n";
    chomp (@data = <DATA>);
}

is_deeply (\@data, \@want);

__DATA__
This is a test.
XXX
This is a multiline
test.
XXX

[Anonymous Monk]

Of course chomp removes $INPUT_RECORD_SEPARATOR! Thank you, hippo.

[tybalt89]

#!/usr/bin/perl

# https://perlmonks.org/?node_id=1223630

use strict;
use warnings;
use Data::Dumper;
$Data::Dumper::Indent = 0;

local $/ = "\nXXX\n";
s/\nXXX\n\z//, tr/\n/ / for my @data = <DATA>;

print Dumper \@data;

__DATA__
This is a test.
XXX
This is a multiline
test.
XXX

[navalned]

I don't generally like statement modifiers. However, this does exactly what I need. I think my main issue was I forgot while slurping my /^XXX$/ probably didn't work and I should have changed it to /\nXXX\n/.

[Laurent_R]

I don't generally like statement modifiers.

You don't have to follow me on that, but statement modifiers can help making your code clearer and more concise.

Consider for instance this (somewhat meaningless) example:

while (<$IN>) {
    next if /^\s*$/;   # remove empty lines
    next if /^\s*#/;   # remove comments
    next if /ORA/i;    # remove lines with Oracle warnings and errors
    next unless some_condition($_);
    last if /File processed/;
    # ... now do the actual processing of useful lines
}

If you wanted to do the same with regular conditionals, you would need about three times as many code lines, and it would probably end up being less clear.

Update: added a missing closing parenthesis to the while condition.<\small>

[jwkrahn]

use strict;
use warnings;

use Data::Dumper;
$Data::Dumper::Indent = 0;

my $file = 'test';
my @data;

{
    local $/;
    open my $FILE, '<', $file or die "Cannot open '$file' because: $!"
+;

    @data = grep /\S/, split /XXX\n/, <$FILE>;
}

print Dumper \@data;

[navalned]

This works great! Thanks!!

[eyepopslikeamosquito]

I would write it something like this:

use strict;
use warnings;

use Data::Dumper;
$Data::Dumper::Indent = 0;

my $file = "test";

# Use lexical file handles and 3-argument form of open
# See http://modernperlbooks.com/mt/2010/04/three-arg-open-migrating-t
+o-modern-perl.html
open my $fh, '<', $file or die "error opening '$file': $!";

# Slurp file contents into string $contents
# See http://modernperlbooks.com/mt/2009/08/a-one-line-slurp-in-perl-5
+.html
my $contents = do { local $/; <$fh> };
close $fh;

# Split contents into fields by XXX on a line by itself (note the /m m
+odifier)
my @fields = split /^XXX$/m, $contents;

# Tidy up newlines/spaces in multiline fields
for (@fields) { tr/\n/ /s; s/^ +//; s/ +$//; }

print Dumper \@fields;

Update: See Also

• Lexical file handles - Perl Maven
• 3-argument form of open - Effective Perl (item 52)
• File slurping - Re: Re: Slurp a file by merlyn

[Marshall]

When you undef the input record separator, you will get the whole input file. I don't think that is the best way. Note that the line endings (\n) would be included in this, that's why you need your grep on non-white space.

I am not at a computer where I can test, but is something like this what you want? Untested:

while (my $line = <$input>)
{
   if ($line =~ /^XXX$/)
   {
      print "\n";
   }
   else
   {  
      chomp $line;
      print $line;
    }
}
print "\n"; #may need a final one of these

In general, I prefer to process files line by line instead of creating an in memory copy of the whole thing, but with computer memory what it is nowadays, this doesn't matter so much.

[Anonymous Monk]

Use the built-in Perl feature for input record separator splitting, perhaps?

use warnings;
use strict;
use Data::Dumper;
{
        local $/ = "\nXXX\n";
        while (my $record = <DATA>) {
                # remove the separator from the record
                $record =~ s{\Q$/\E$}{};
                print Dumper $record;
                # process the record here
        }
};
__DATA__
This is a test.
XXX
This is a multiline
test.
XXX

$VAR1 = 'This is a test.';
$VAR1 = 'This is a multiline
test.';

This may be useful if your file becomes impractical to fit in the RAM and you only need to process it record-by-record.

[navalned]

This works really well. Thanks!

[Anonymous Monk]

hippo's answer Re: breaking up a file by delimiter presents a better way to remove input record separators from strings. No need for regexps here.