#!/usr/bin/perl

use strict;
use warnings;

use IPC::System::Simple qw( capturex );

sub get_data {
    my ($pattern) = @_;
    return capturex('grep', $pattern, '/etc/passwd');
}

my @ids = qw( john james );

{
   # Assumes each of @ids are "safe".
   my $pattern = '^\\(' . join('\\|', @ids) . '\\)';
   my $permission = get_data($pattern);
   print($permission);
}

{
   # Assumes each of @ids are "safe" and match /^\w/ and /\w\z/.
   my $pattern = '\b\\(' . join('\\|', @ids) . \\)\b';
   my $permission = get_data($pattern);
   print($permission);
}