I want to run the su command as

#su - saif -c "/script/start.pl redhat redhat1 redhat1"

but start.pl cannot get these 3 parameter i.e. "redhat redhat1 redhat1".

any help please my start.pl is

#!/usr/bin/perl

my $oldpw = $ARG[0];
my $newpw_1 = $ARG[1];
my $newpw_2 = $ARG[2];
my $smbpasswd = "/usr/bin/smbpasswd";

&pw_change($smbpasswd,$username,$oldpw,$newpw_1,$newpw_2);

sub pw_change(){
my ($smbpasswd,$username,$oldpw,$newpw_1,$newpw_2) = @_;

if ( "$newpw_1" eq "$newpw_2" ) {

open (FILE, "|$smbpasswd -s") or die("cannot pipe into $smbpasswd: $!");

print FILE qq|$oldpw\n|;
print FILE qq|$newpw_1\n|;
print FILE qq|$newpw_1\n|;
close (FILE);
}
}

1. Show the exact error msg you're getting.
2. Even better, tell the prog to print those valuse as soon as it has read them.
3. The '&' is deprecated for calling a sub in Perl 5; it technically means pass ref-to-sub. Just use subname($param1,$param2,..).
4. Try

#!/usr/bin/perl -w
use strict;