SPUG: Should I not do while (<FOO> !~ /^mailboxes/) { } ?

[Chris Wilkes]

Hello everyone,

  I wanted to read in a mutt configuration file and only pull out one of
the lines that starts with mailboxes so I did this:
	#!/usr/bin/perl -w
	$file = ".muttrc";
	open (FOO, $file) || die "Can't open $file\n";
	while (<FOO> !~ /^mailboxes/) {
	  print "#$_\n";
	}
	close FOO;
	print "$_\n";
  To my surprise just a bunch of pound signs show up.  $_ has been
replaced with nothing in the loop; also exiting the loop $_ is set to
nothing.  There are warnings about "use of an uninitialized value in
concatentation"
  Then I decided to go about the easy way of fixing this:
	while (($in = <FOO>) !~ /^mailboxes/) { }	# Style 2
  which gave me $in on the exit.  However being the experimental type I
decided to do this:
	while (($_ = <FOO>) !~ /^mailboxes/) { }	# Style 3
  now in the loop and exiting $_ is set to the right thing, that is each
line of the .muttrc file.
  I think the warning happens as the magic variable <FOO> doesn't match
^mailboxes so it complains on the "print $_" line as there is nothing in
there.  However it does exit at the right time when it hits ^mailboxes
so I would expect it to be in $_ upon exit.
  Can someone shed some light on this?
  Also when I did this with <DATA> and __DATA__ instead of the
filehandle FOO it complains about a pattern match in addition to the
concatenation error when doing it in Style #3, where it didn't complain
before with the opened file.  The script also loops on forever if it
can't (not) match the ^mailboxes.:
	#!/usr/bin/perl -w
	while (($_ = <DATA>) !~ /^mailboxes/) {
	  print "#$_\n";
	}
	__DATA__
	The quick brown fox
	jumped over
	the lazy dog
  That boggles me too.

Chris

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