#!/usr/bin/perl
# vi:ts=4 sw=4 et:
use strict;
use warnings;

my $file = '/etc/passwd';

open my $infh, $file or die "$file: $!\n";
my @passwd = <$infh>;
close $infh or die "$file: $!\n";

for my $i ( 0 .. $#passwd ) {
    
    $passwd[$i] =~ s{/bin/(.+)$}{/bin/false};

    print $passwd[$i];

}

# BACKUP /etc/passwd; THEN something like
open my $outfh, '>', $file or die "$file: $!\n";

print $outfh @passwd or die "$file: $!\n";
close $outfh or die "$file: $!\n";

__END__