Perl脚本错误：perl中未初始化的值错误

Question

我收到以下错误：

“在连接中使用uninitatlize value $ gi＆lt;。＆gt;或在fillename.pl第32行第4行使用字符串。”

对于所有打开的文件重复此消息，但第一行后第5行换行。

我无法确定如何修复它！我打开的文件是标准的fasta文件，格式如下，第一行包含序列信息，后面的行是序列。 这是我的代码

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

#open files from data directory
opendir my $data_dir, "data" or die "Unable to open directory!";
my @files = readdir $data_dir;    #reading files into array

#Taking only files with .fa extention
my @fa_files = grep /\.fa$/, @files;
my @sorted_fa_files = sort @fa_files;

#Taking each .fa and reading description line
foreach my $filename (@sorted_fa_files) {
    open my $filehandle, "<", "data/$filename" or die "Unable to open file!";

    while ( my @file_contents = <$filehandle> ) {    #setting aray to contain all file contents
        chomp @file_contents;
        print "filename: $filename\n";

        my $description_line = shift @file_contents;    #setting array to contain description line only
        my $join_seq = join "", @file_contents;

        #extracting description line contents individually
        my @description_parts = split /[\|\.]/, $join_seq;
        foreach (@description_parts) {
            my $gi              = $description_parts[1];
            my $accession_id    = $description_parts[3];
            my $version         = $description_parts[4];
            my $seq_description = $description_parts[5];
            print "gi number: $gi\n";
        }

    }
}