How can I write XML data to a file with Perl?

Question

Could you please correct my code below.

#!/usr/local/bin/perl

open (MYFILE, '>>data.xml');
print MYFILE "<?xml version="1.0" encoding="UTF-8"?>\n";
close (MYFILE); 

Updated.

#!/usr/local/bin/perl
open (MYFILE, '>>data.xml');
print MYFILE '<?xml version="1.0" encoding="UTF-8"?\>'."\n";
print MYFILE '<?xml version="1.0" encoding="UTF-16"?\>'."\n";
close (MYFILE);

output: working well now.

<?xml version="1.0" encoding="UTF-8"?\>
<?xml version="1.0" encoding="UTF-16"?\>

BUT.

#!/usr/local/bin/perl
open (MYFILE, '>>data.xml');
print MYFILE '<?xml version="1.0" encoding="UTF-8"?\>'.'\n';
print MYFILE '<?xml version="1.0" encoding="UTF-16"?\>'.'\n';
close (MYFILE);

Output: # error format with \n

<?xml version="1.0" encoding="UTF-8"?\>\n<?xml version="1.0" encoding="UTF-16"?\>\n

Answer 1

The problem is you have unescaped quotes in the string. Either escape the quotes using the backslash or surround your print string with qq{}:

print MYFILE qq{<?xml version="1.0" encoding="UTF-8"?>\n};
--or--
print MYFILE "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";

Answer 2

print MYFILE qq{<?xml version="1.0" encoding="UTF-8"?>\n};

Your problem is that you had nested double quotes; using qq{} to delimit the string will solve this issue.

Answer 3

Always turn on warnings and strictures, so you find out earlier what went wrong, and get more details why:

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

Always use the lexical-variabled, three-argument form of open (there's a big discussion why over here), and always check the return value (it will return an error if something went wrong, and put the reason why in the $! variable (see under $! at perldoc perlvar). Also, die will print the line number of where the program quit if you don't end your string with a \n (more at perldoc -f die).

open my $file, '>>', 'data.xml' or die "Can't open file: $!";

And use double-quotes around the \n so that it is printed properly:

print $file '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
print $file '<?xml version="1.0" encoding="UTF-16"?>' . "\n";
close $file;

Answer 4

I would recommend to use:

use XML::Simple;

Answer 5

Here is some code of mine for printing an XML file:

open(XML, ">$xmlfile");
print XML (<<EOF);
<?xml version="1.0" encoding="UTF-8"?>
<gpx
 version="1.1"
 creator="Navaid Waypoint Generator - http://navaid.com/GPX/"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns="http://www.topografix.com/GPX/1/1"
 xmlns:navaid="http://navaid.com/GPX/NAVAID/1/0"
 xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd
 http://navaid.com/GPX/NAVAID/1/0 http://navaid.com/GPX/NAVAID/1/0">
 <metadata>
    <author>
        <name>Paul Tomblin</name>
        <email id="ptomblin" domain="xcski.com"/>
        <link href="http://blog.xcski.com/"/>
    </author>
    <link href="http://navaid.com/GPX/"/>
</metadata>
EOF

Answer 6

Always, always, ALWAYS check the value returned from open, e.g.,

open (MYFILE, '>>data.xml')
  or die "$0: open: $!";

Note the important bits in the error message:

1. the name of the program that failed, $0
2. what it was trying to do, open
3. why it failed, $!

Without a newline at the end of the string passed to die, it appends the file and line number where your program died.

Answer 7

If you want to write UTF-8 data to a file (as you say in your XML declaration, open the file with a UTF-8 encoding:

open my($fh), '>:utf8', 'data.xml' or die "Could not open file: $!";

print $fh qq{<?xml version="1.0" encoding="UTF-8">\n};

Answer 8

Several additional points of advice:

• For writing complex, structured files, use a library like XML::Simple or one of the many, many others available on CPAN.

• If you are writing many very similar files, a templating module may be more appropriate.

• Take Ether's advice re: open, strict and warnings. It will save you time debugging.

• If you are going to claim that a file has a particular encoding (UTF-8 or UTF-16), you probably should emit actual Unicode text to the file. There is more info in perldoc -f open.