open to a scalar variable

girarde has asked for the wisdom of the Perl Monks concerning the following question:

Per the open manpage, I am attempting to open a filehandle to a variable in memory and I am unable to read the variable. My code looks like this:

open(MESSAGE, "+>>", "\$message") or die "no message $!";

open(WHOM, ">>", "&=MESSAGE") or die "no whom $!";

open (WHAT, ">>", "&=MESSAGE") or die "no what $!";
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after which much is written to the handles using various formats, and an attempt to get the data is made so:

while (my $line = <MESSAGE>) {
    print $line;
    $text .= $line;
}

print $text;
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The result is:

Use of uninitialized value in print at check_remove.pl line 85.

where line 85 is the print $text line. Opening MESSAGE in different modes does not yield better results. For instance, using the syntax in the open manpage results in a Filehandle MESSAGE opened only for output error. It works OK if I omit the handles and point the formats at STDOUT, but I am on Win32 and want to mail the output, so piping the output to SENDMAIL won't help. I was going to use Mail::Sendmail, which is why I want the output in a scalar. What am I missing?

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Re: open to a scalar variable by kyle (Abbot) on Jun 04, 2007 at 21:53 UTC
Don't put quotes around the variable (see open). `open(MESSAGE, '+>>', \$message) or die "no message $!";` [download] (What you're doing is opening a file literally named "`$message`".)	[reply] [d/l] [select]
Re^2: open to a scalar variable by girarde (Hermit) on Jun 05, 2007 at 13:56 UTC
Unquoting `\$message` yielded an "uninitialized value" error at the print statement.	[reply] [d/l]
Re^3: open to a scalar variable by kyle (Abbot) on Jun 05, 2007 at 14:17 UTC
Putting together some of the other suggestions in this thread, I come up with this: `my $message = ''; open(MESSAGE, '+>>', \$message) or die "no message $!"; open(WHOM, '>>&=MESSAGE') or die "no whom $!"; open(WHAT, '>>&=MESSAGE') or die "no what $!"; print WHOM "I say 'whom'\n"; print WHAT "I say 'what'\n"; my $text; while (my $line = <MESSAGE>) { print $line; $text .= $line; } print $text; __END__ I say 'whom' I say 'what' I say 'whom' I say 'what'` [download]	[reply] [d/l]
Re: open to a scalar variable by almut (Canon) on Jun 04, 2007 at 22:35 UTC
and an attempt to get the data is made so: ... Why do you need to get at the data in `$message` by reading from the associated filehandle? (seems like a rather cumbersome way to copy a string from one variable to another... :) But if you really insist on doing that way, I suppose you have to reset the filepointer to the beginning before reading, e.g. `use strict; use warnings; open my $msg, "+>", \my $message or die "no message $!"; print $msg " foo\n"; print $msg " bar\n"; print "\$message:\n$message"; seek $msg, 0, 0; # reset filepointer my $text; while (my $line = <$msg>) { $text .= $line; } print "\$text:\n$text";` [download] Output: `$message: foo bar $text: foo bar` [download] In other words, once you have the mail in `$message`, why not pass it directly to `Mail::Sendmail`...	[reply] [d/l] [select]
Re^2: open to a scalar variable by girarde (Hermit) on Jun 05, 2007 at 14:04 UTC
It turns out that once the filehandles are working properly I don't need to read from the filehandle, I can just read `$message` normally. Thank you.	[reply] [d/l]
Re: open to a scalar variable by kwaping (Priest) on Jun 04, 2007 at 21:55 UTC
I'm not very familiar with this technique, but try this instead: `open(MESSAGE, "+>>", \$message) or die "no message $!"; open(WHOM, ">>&=", MESSAGE) or die "no whom $!"; open (WHAT, ">>&=", MESSAGE) or die "no what $!";` [download] If `$message` is already a reference, try dropping the backslash too. --- It's all fine and dandy until someone has to look at the code.	[reply] [d/l] [select]
Re^2: open to a scalar variable by girarde (Hermit) on Jun 05, 2007 at 14:04 UTC
`$message` is declared but not defined until the reference assignment is made. Anyway, unquoting `$message` and putting the `&=` into the mode argument worked. Thank you.	[reply] [d/l] [select]