Question

I am currently trying to set a debug flag using command-line arguments in Perl and I seem to be having problems with something which I thought was pretty easy.

    my $debugvalue;

    my $file = $ARGV[0] or die;

    if ($ARGV[1] == "debug")
    {
        $debugvalue = 1;
    }else
    {
        $debugvalue = 0;
    }

I am looking to enter a file followed by a word purely saying debug, if it doesn’t then set the flag to 0.

test.pl file.txt debug

• Would set the flag to 1

  test.pl file.txt debug

• Would set the flag to 0

I would assume this how you do this, except whatever is inputted, it always drops into the first part of the if and sets the flag to 1.

Answer 1

That would work fine, but you need to use the string comparison, eq, rather than numeric comparison, ==.

if ($ARGV[1] eq "debug")

Also, you can shorten that up to just:

my $debugvalue = $ARGV[1] eq "debug";

In general, I prefer to use the environment for debug settings, though.

my $debugvalue = $ENV{DEBUG} || 0;

Then you can do things like:

DEBUG=1 test.pl file.txt

or set the test on for every run in bash or zsh:

export DEBUG=1
test.pl file.txt
test.pl file2.txt
test.pl file3.txt

or even have more than one debug level if you need aggressive debugging output to help diagnose a particular problem:

DEBUG=3 test.pl file.txt

and in your code:

warn "Fiddly Detail $x\n" if $debugvalue > 2;