#!/usr/bin/env perl
use warnings;
use strict;
use File::Copy;
use File::Find;

my $dir = '/home/oo/bin';

find( \&wanted, $dir );

sub wanted {
    my $file = $File::Find::name;
    if ( -e $file and -f $file ) {
        my $temp = 'temp_file';
        open my $out, '>', $temp or die $!;
        open my $in, '<', $file or die $!;
            while ( defined( my $row = <$in> ) ) {
                $row =~ s|^#!/usr/bin/perl|#!/usr/bin/env perl|;
                print $out $row;
            }
        close $in or die $!;
        close $out or die $!;
        move $temp, $file or die $!;
        chmod 0755, $file or die $!;
    }
}