Shell Programming and Scripting

I copy and paste from the book but this thing is not working.

I cannot figure out what is wrong with myline 9.. can someone please tell me



[root@localhost perl]# cat ./sort4.pl
#!/usr/bin/perl -w

use strict;
use warnings;

my $input = shift;
my $output = shift;

open(IN, '<', $input) or die "Can't read source file $input: $!\n";
open(OUT, '>', $output) or die "CAn't write to file $output: $!\n";

my @file = <IN>;
@file = sort @file;

print OUT @file;

close IN;
close OUT;

[root@localhost perl]# perl -c sort4.pl
sort4.pl syntax OK

[root@localhost perl]# perl sort4.pl
Use of uninitialized value in open at sort4.pl line 9.
Use of uninitialized value in concatenation (.) or string at sort4.pl line 9.
Can't read source file : No such file or directory

$input is not defined

defined($input);

Code:

    my $input = 'foo.txt';
    my $output = 'bar.txt';

    open IN, "< $input" or die "Can't open $input : $!";
    open OUT, "> $output" or die "Can't open $output : $!";
    print OUT <IN>;
    close IN;
    close OUT;

or use @ARGV to define files

if you want to use shift try something like

Code:

sub doit {
    my $input = shift;
    my $output = shift;

    open IN, "< $input" or die "Can't open $input : $!";
    open OUT, "> $output" or die "Can't open $output : $!";
    print OUT <IN>;
    close IN;
    close OUT;
}

doit('foo.txt','bar.txt');

But this example were taken from a book called "begining perl".. I don't understand where I made a mistake...

try calling the program as

perl program.pl input.txt output.txt

that works.. I guess perl programname does not work, if you don't give all the argument?