foreach ($a, $b)
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while (<$fh>)
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So what output did you get?

It might help to verify the return value of open, as in, "open $fh, '<', $_ or die $!;" so you'll know if the open is failing.

when i run code i get two warning
Use of uninitialized value $a in print at D:\test.pl line 38.
Use of uninitialized value $b in print at D:\test.pl line 38.

I only see 19 lines of code. Which line is #38?

Update: Thanks for clarifying your code now.

Your while loop is reading <$fh> into $_, which is clobbering your foreach loop's version of $_. Since the topic variable in a foreach loop aliases the elements you're iterating over (ie, $a and $b), clobbering $_ clobbers $a and $b.

Use an explicitly named topic variable for your foreach loop.




Dave

while(<$fh>)
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while(defined($_ = <$fh>))
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and $_ is aliased to $a and $b in turn by the foreach loop. Every time you change $_ by assigning a line to it, you change the value of $a or $b.

Solution: Change

    while(<$fh>){
        print;
    }
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to

    local $_;
    while(<$fh>){
        print;
    }
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or

    while(my $line = <$fh>){
        print $line;
    }
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By the way, because $a and $b have special meaning to sort, one usually avoids them. my $a and my $b can actually cause sort to malfunction.

I don't know what's causing this, but you should stay away from $a and $b as variable names, as they are reserved for sort (perlvar).

Furthermore, I don't understand why you are using unix commands in system() despite running on windows.

the question is not the variable's name.
when i change variable name warning still exist
install gnuwin32 you can use ls command in windows

FWIW, using $a and $b outside of sort is always a mistake