This behavior is certainly not obvious and it is not (clearly) documented either under 'perldoc -f glob' or at perldoc.perl.org. The line saying "In scalar context, glob iterates through such filename expansions, returning undef when the list is exhausted" does not make it clear (at least to me) that such a state persists across calls to glob with a new argument!

I agree that the docs for glob (perldoc -f glob) are not clear. When I read the docs for glob, and I came upon the sentence:

In scalar context, glob iterates through such filename expansions, returning undef when the list is exhausted.

I had no idea what that meant. However, I immediately recognized that that sentence did NOT mean what you claimed it meant, namely that in scalar context glob returns true if there were any matching files. I have no idea how you arrived at that interpretation. In my opinion, the literal interpretation would be that in scalar context, glob() sits for a few seconds as it spins through the list of matches, and then glob returns undef, i.e. glob always returns undef in scalar context.

In any case, after reading the docs I was prompted to try an experiment to see how glob() works in scalar context. So I setup this directory structure:

/some_dir
   my_prog.pl
   dir1/
      a.txt
      b.txt
      f1.txt
      f2.txt
   dir2/
   dir3/
      x.txt
      y.txt

And then I ran this code:

use strict;
use warnings;
use 5.012;

while (my $x = glob "dir1/f*") {
    say $x;
}

--output:--
dir1/f1.txt
dir1/f2.txt
[download]

After examining the output, I quickly understood how glob() works in scalar context. To be clearer, the docs should say something like this:

In scalar context, glob returns the next filename from the list of matching filenames or undef if the list has been exhausted.

Edit-- so that statement should have some qualifications:

In scalar context:

1. Inside a loop: glob returns the next filename from the list of matching filenames, or undef if the list has been exhausted--with the next call to glob returning the first matching filename again.
2. Outside a loop: glob() always returns the first matching filename.

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.