using perl tie::file with utf encoded file

3
votes

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");
3
perl

3 Answers

5
votes

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)

4
votes
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.)

4
votes

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