Shell Programming and Scripting

in windows machine...

C:\2\test>perl -version

This is perl, v5.6.1 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)
------------------------------------------
what is the difference b\w subroutine calls:

sub_routine_name("-----");

and

&sub_routine_name("-----");

thanks,

normally a sub can be called like a function - without the & in front as long as you have the ( ) part at the end so the interpreter can figure out it's a subroutine.

You must have the & when:
you call a subroutine without parameters: ⊂
you call a subroutine indirectly by name &$subref(args);
you call a subroutine by reference &$subref;

The fact is a little bit more complicated.

The ( ) can be omitted as well, as long as the subroutine has already been defined at the point of the call.

Code:

#!/usr/bin/perl -w

use strict;

sub echo {
    my $str = shift;
    print $str if (defined $str);
}

echo;
echo "Hello World!\n";

will not give any warnings at all. But if you put the sub at the bottom:

Code:

#!/usr/bin/perl -w

use strict;

echo;
echo "Hello World!\n";

sub echo {
    my $str = shift;
    print $str if (defined $str);
}

The solitary "echo;" will give an error for bareword usage (if you remove the use strict, it will be a warning instead). If you place the & back in, it will now be okay:

Code:

#!/usr/bin/perl -w

use strict;

&echo;
echo "Hello World!\n";

sub echo {
    my $str = shift;
    print $str if (defined $str);
}

So to "&" or not sometimes depends on the order you define and use subroutine and their references. For the other case, see below.

Also note that in these two cases the current @_ as a list of params will be passed to the called subroutine. So

⊂
&$subref;

is the same as

sub(@_); OR &sub(@_);
&$subref(@_);

but not the same as

&sub();
&$subref();

respectively.

See perlsub manpage for total treatment of the subject.