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

[Dean Hudson]

If you want $_ to get set you should probably do something more like:

while (<FOO>) {
    next if /^mailboxes/;
}

while (<FOO> !~ /^mailboxes/) does not set implicitly set $_ the way
you hope.

It's not really clear to me what you're trying to do exactly. Do you
want to print the mailboxes line with a prepended # or the other lines
with a # prepended.

Here's another way you could do either:

dean at apogee:~ > perl -e 'grep {/^mailboxes/ && print "#$_" } <>';
this
is
a
test
mailboxes
test
#mailboxes

dean at apogee:~ > perl -e 'grep {!/^mailboxes/ && print "#$_" } <>';
this
is
a
test
mailboxes
test
#this
#is
#a
#test
#test
dean at apogee:~ >

dean.

On Fri, Feb 22, 2002 at 02:11:44PM -0800, Chris Wilkes wrote:
> 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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     POST TO: spug-list at pm.org       PROBLEMS: owner-spug-list at pm.org
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  Replace ACTION by subscribe or unsubscribe, EMAIL by your Email-address
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