http://qs321.pair.com?node_id=1187675


in reply to Strange behaviour when using glob in if condition

I looked into this further and was able to reproduce the issue using your code, and find an explanation and workaround. glob in scalar context acts like an iterator. However, the iterator state is attached to the glob call site, even when the argument to glob changes. Here's a simple way to reproduce the issue:

$ touch foo bar $ perl -MData::Dump -e ' sub myglob {scalar glob($_[0])} dd myglob($_) for qw/foo bar/ ' "foo" undef

One might expect the output here to be "foo" and "bar". There is an excellent discussion in RT#123404, and it doesn't sound like this behavior is going to change, as potentially confusing as it is.

A simple workaround is to force list context:

return if ()=glob("$directory/*");

Replies are listed 'Best First'.
Re^2: Strange behaviour when using glob in if condition
by LanX (Saint) on Apr 11, 2017 at 21:25 UTC
    Brilliant analysis!

    Sounds like we need a warning if glob is used in scalar context with a pattern holding interpolated variables. :/

    I for my part will now only use for glob() constructs for looping over a static list.

    Cheers Rolf
    (addicted to the Perl Programming Language and ☆☆☆☆ :)
    Je suis Charlie!