I managed to get caught out the other day writing something that amounted to the following code. 
#!/usr/bin/perl -w 
use strict;

open (IN, "file1") or die("can't blah blah");
while (<IN>) {
    print;
    print slurp();
}
sub slurp {
    my $slurp = do { local $/ = undef; open IN, "file2"; <IN>};
    return $slurp;    
}

[download]
Can you spot it? Yeah, of course you can, but my code was a bit more involved than this ;). To clarify, what happens is as follows. The first 'while' successfully reads the first line of file1. It prints this line, then the slurp returns file2, and its contents are also printed. Unfortunately, because I used the same file handle, the while thinks its at the end of file1 and and skips to the end.

Okay fair enough, filehandles appear to be global, my stupid mistake, but my question is this...

Can I avoid ever making this mistake again?

Should I always 'use FileHandle'? Is this a bit over the top, or worth the effort? It would have been nice if I'd been given some warning too. :)

I'd be interested to hear if others have been caught out by this, and what you're doing now to avoid the same.

---
my name's not Keith, and I'm not reasonable.

In reply to Filehandles, scope and warnings. by reasonablekeith

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