Given The user will be in the directory their answer file is located,

my $file_name = @ARGV ? shift(@ARGV) : 'answerfile';
open(my $fh, '<', $file_name)
   or die("Unable to open answer file \"$file_name\": $!\n");
[download]

If you wanted to know the full path,

use File::Spec::Functions qw( rel2abs );

my $full_name = rel2abs($file_name);
[download]

If you wanted to know the directory,

use File::Basename qw( dirname );

my $dir_name = dirname($full_name);
[download]

Update: Here it is in practice:

E:\some\path>type ..\bin\routine.pl
use strict;
use warnings;

use File::Basename        qw( dirname );
use File::Spec::Functions qw( rel2abs );

my $file_name = @ARGV ? shift(@ARGV) : 'answerfile';
open(my $fh, '<', $file_name)
   or die("Unable to open answer file \"$file_name\": $!\n");

my $full_name = rel2abs($file_name);
my $dir_name  = dirname($full_name);

print("Name:      $file_name\n");
print("Full Name: $full_name\n");
print("Dir Name:  $dir_name\n");
print("Contents:\n");
print while <$fh>;

E:\some\path>type answerfile
Answer file in \some\path

E:\some\path>type ..\otherpath\answerfile
Answer file in \some\otherpath

E:\some\path>..\bin\routine.pl
Name:      answerfile
Full Name: E:\some\path\answerfile
Dir Name:  E:\some\path
Contents:
Answer file in \some\path

E:\some\path>..\bin\routine.pl ..\otherpath\answerfile
Name:      ..\otherpath\answerfile
Full Name: E:\some\path\..\otherpath\answerfile
Dir Name:  E:\some\path\..\otherpath
Contents:
Answer file in \some\otherpath

E:\some\path>..\bin\routine.pl e:\some\otherpath\answerfile
Name:      e:\some\otherpath\answerfile
Full Name: E:\some\otherpath\answerfile
Dir Name:  E:\some\otherpath
Contents:
Answer file in \some\otherpath
[download]

I used windows, but it works without changes in unix.

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