using perl tie::file with utf encoded file - perl

Question

Can I use Tie::File with an output file of utf encoding? I can't get this to work right.
What I am trying to do is open this utf encoded file, remove the match string from the file and rename the file.
Code:
use strict;
use warnings;
use Tie::File;
use File::Copy;
my ($input_file) = qw (test.txt);
open my $infh, "<:encoding(UTF-16LE)", $input_file or die "cannot open '$input_file': $!";
for (<$infh>) {
tie my #lines, "Tie::File", $_;
shift #lines if $lines[0] =~ m/MyHeader/;
untie #lines;
my ($name) = /^(.*).csv/i;
move($_, $name . ".dat");
}
close $infh
or die "Cannot close '$input_file': $!";
Code: (updated)
my ($input_file) = qw (test.txt);
my $qfn_in = $input_file;
my $qfn_out = $qfn_in . ".dat";
open(my $fh_in, "<:raw:perlio:encoding(UTF-16le):crlf:utf8", $qfn_in)
or die("Can't open \"$qfn_in\": $!\n");
open(my $fh_out, ">:raw:perlio:encoding(UTF-16le):crlf:utf8", $qfn_out)
or die("Can't open \"$qfn_out\": $!\n");
while (<$fh_in>) {
next if $. == 1 && /MyHeader/;
print($fh_out $_)
or die("Can't write to \"$qfn_out\": $!");
}
close($fh_in);
close($fh_out) or die("Can't write to \"$qfn_out\": $!");
rename($qfn_out, $qfn_in)
or die("Can't rename: $!\n");

Answer 1

This is underdocumented in the Tie::File perldoc, but you want to pass the discipline => ':encoding(UTF-16LE)' option when you tie the file:
tie my #lines, 'Tie::File', $input_file, discipline => ':encoding(UTF-16LE)'
Note that the third argument is the name of the file to associate with the tied array. Tie::File will automatically open and manage the filehandle for you; there is no need to call open on the file yourself.
#lines now contains the contents of the file, so the next thing to do is check the first line:
if ($lines[0] =~ m/pattern/) {
my $line = shift #lines;
untie #lines; # rewrites, closes the file, w/o first line
my ($name) = $line =~ /^(.*).csv/i;
rename $input_file, "$name.dat";
}
But I concur with TLP that Tie::File is overkill for this job.
(My previous answer about opening a filehandle with the correct encoding and passing the glob as the third arg to Tie::File won't work, as (1) it didn't open the file in read/write mode and (2) even if it did, Tie::File can't or doesn't apply the encoding on both the reading from and writing to the file handle)

Answer 2

my $qfn_in = ...;
my $qfn_out = $qfn_in . ".tmp";
open(my $fh_in, "<:raw:perlio:encoding(UTF-16le):crlf:utf8", $qfn_in)
or die("Can't open \"$qfn_in\": $!\n");
open(my $fh_out, ">:raw:perlio:encoding(UTF-16le):crlf:utf8", $qfn_out)
or die("Can't open \"$qfn_out\": $!\n");
while (<$fh_in>) {
next if $. == 1 && /MyHeader/;
print($fh_out $_)
or die("Can't write to \"$qfn_out\": $!");
}
close($fh_in);
close($fh_out) or die("Can't write to \"$qfn_out\": $!");
rename($qfn_out, $qfn_in)
or die("Can't rename: $!\n");
(:perlio and :utf8 are workarounds for bugs that existed back then.)

Answer 3

The line:
tie my #lines, "Tie::File", $_;
Tries to tie #lines to a file with the name of each line of test.txt. Since it does not seem to be a file with filenames in it, I suspect that that tie fails.
What you are probably after is using Tie::File on test.txt. If you only want to check the first line of that file, you do not need a loop.
So you'd need something like:
use autodie; #handy to check for fatal errors
tie my #lines, "Tie::File", $input_file;
shift #lines if $lines[0] =~ /MyHeader/;
untie #lines;
if ($input_file =~ /(.+).csv/i) {
move($input_file, $1);
}
But there are simpler ways to check the first line of a file. This will check one file:
perl -we '$_=<>; print if /MyHeader/; print <>;' test.txt > test.dat