#!/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);
}

##</code><code>##

#!/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);
}

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

sub get_etc_passwd {
    open(my $fh, '<', '/etc/passwd') or die $!;
    return <$fh>;
}

my @ids = qw( john james );
my @etc_passwd = get_etc_passwd();

{
   my $pattern = join('|', map quotemeta, @ids);
   my $re = qr/^(?:$pattern)/;
   print(grep /$re/, @etc_passwd);
}

{
   my $pattern = join('|', map quotemeta, @ids);
   # Assumes each of @ids match /^\w/ and /\w\z/.
   my $re = qr/\b(?:$pattern)\b/;
   print(grep /$re/, @etc_passwd);
}