#!/usr/bin/perl

use strict;
use warnings;

sub text_to_shell_lit(_) {
   return $_[0] if $_[0] =~ /^[a-zA-Z0-9_\-]+\z/;
   my $s = $_[0];
   $s =~ s/'/'\\''/g;
   return "'$s'";
}

sub get_data {
    my ($pattern) = @_;
    my $pattern_lit = text_to_shell_lit($pattern); 
    return qx( grep $pattern_lit /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);
}