numbering lines problem

[WisDomSeeKer34]

I was advised to come here: http://www.linuxquestions.org/questions/showthread.php?p=5271797#post5271797
This is the code:

#!/usr/bin/perl

use warnings;

for ($x = 1; $x < 10; $x++) {

if ($_ =~ /^\d/) {$y = $y + 1;}    # if the line does start with a num
+ber, ignore it. 
if ($_ != /^\d/) {print $y.$x;}    # if the line doesn't start with nu
+mber then print numbers.
}

After running it:  perl counting.pl python.txt I get the following error:
Use of uninitialized value $_ in pattern match (m//) at counting.pl line 7.
Use of uninitialized value $_ in pattern match (m//) at counting.pl line 8.
Use of uninitialized value $_ in numeric ne (!=) at counting.pl line 8.
etc.

Purpose of the program is to line numbers according to chapter:
1.
1.1
1.2
2.
2.1
2.2

[toolic]

http://www.linuxquestions.org/questions/showthread.php?p=5271797#post5271797

Here is a self-contained version. As pan64 noted, you need to get your lines of input from somewhere (this is why $_ is uninitialized). You should just be able to use while (<>) { to read in from your python.txt file.

use warnings;
use strict;

my $chap;
my $sect;
while (<DATA>) {
    if (/^(\d+)/) {
        $chap = $1;
        $sect = 0;
    }
    else {
        $sect++;
        s/^/$chap.$sect /;
    }
    print;
}

__DATA__
1. Operators
Performing simple arithmetic
Operating on bitwise values
Comparing values
Operating on Boolean values
Operating on parts of a container with the slice operator
Understanding operator precedence
2. Regular Expressions
Using the re module
Searching with regular expressions

See also: perlintro

[WisDomSeeKer34]

Reading your code, it seems so obvious. Thank you.

[AnomalousMonk]

if ($_ != /^\d/) {print $y.$x;}    # if the line doesn't start with number then print numbers.


For future reference, also note that  !~ is "negated match", whereas  != is numeric not-equal, hence the warning. See perlop.