Keep file open for sub call?

zod has asked for the wisdom of the Perl Monks concerning the following question:

I need to:

1) open a file
2) print stuff to file
3) call a subroutine that also prints to that file

So I thought I ought to do it like this:

my $filepath = 'foo.txt';
open my $FOOFILE, '>>', $filepath or die "Couldn't open $filepath \n";
print $FOOFILE "First line of text.\n";


for ( my $outer_loop = 1 ; $outer_loop <= 5 ; $outer_loop++ ) {

    #do a bunch of stuff

    &do_other_stuff;

    if ( $outer_loop == 5 ) {
        print $FOOFILE "The end.";
        close $FOOFILE;
    }

}

sub do_other_stuff {

    for ( my $inner_loop = 0 ; $inner_loop < 5 ; $inner_loop++ ) {

        if ( $inner_loop == 3 ) {
            print $FOOFILE "A match!\n";
        }

    }
[download]

My question is whether this is poor form. Should I close and reopen the file in the sub instead of just leaving it open? More like this:

sub do_other_stuff {

  open $FOOFILE, '>>', $filepath or die "Couldn't open $filepath \n";

    for ( my $inner_loop = 0 ; $inner_loop < 5 ; $inner_loop++ ) {

        if ( $inner_loop == 3 ) {
            print $FOOFILE "A match!\n";
        }

    }
    close $FOOFILE;
}
[download]

Thanks,

zod

Comment on Keep file open for sub call? Select or Download Code

Replies are listed 'Best First'.
Re: Keep file open for sub call? by GrandFather (Saint) on Nov 20, 2008 at 03:12 UTC
Why not: `my $filepath = 'foo.txt'; open my $FOOFILE, '>>', $filepath or die "Couldn't open $filepath: $!\ +n"; print $FOOFILE "First line of text.\n"; for (1 .. 5) { #do a bunch of stuff do_other_stuff ($FOOFILE); } print $FOOFILE "The end."; close $FOOFILE;` [download] Unless there are multiple applications that may be updating the file and that are fighting for locks on it (in which case you are in a whole other world of pain) there is no reason to close the file. Opening and closing a file can be relatively expensive so avoiding that cost is generally a Good Thing™. Note that you should avoid using global variables in subs ($FOOFILE for example) and generally you shouldn't call subs using the `&sub` syntax. Also, use the Perl for loop rather than the C for loop where you can. Perl reduces RSI - it saves typing	[reply] [d/l] [select]
Re^2: Keep file open for sub call? by zod (Scribe) on Nov 20, 2008 at 03:50 UTC
Thanks for the input.	[reply]
Re: Keep file open for sub call? by lostjimmy (Chaplain) on Nov 20, 2008 at 03:15 UTC
Update: GrandFather beat me to it! In my opinion, I don't think you should close and then reopen the file in the subroutine. The only things I would change would be to pass the file handle to the sub, use foreach style loops rather than the c-style loops you are using (`for my $inner_loop (0..4)`), and change `&do_other_stuff` to `do_other_stuff()`	[reply] [d/l] [select]
Re: Keep file open for sub call? by toolic (Bishop) on Nov 20, 2008 at 14:55 UTC
Assuming the amount of data you are writing to a file is relatively small, another approach is to accumulate the lines of data into an array, then open/write/close the file in one place: `my @lines; push @lines, "First line of text.\n"; # keep pushing lines of text into the array my $filepath = 'foo.txt'; open my $FOOFILE, '>>', $filepath or die "Couldn't open $filepath: $!" +; print $FOOFILE $_ for @lines; close $FOOFILE;` [download] You could pass the array as a reference to your sub.	[reply] [d/l]