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From: merlyn@iwarp.intel.com (Randal Schwartz)
Newsgroups: comp.lang.perl
Subject: Re: Why does my variable keep changing?!!
Message-ID: <1990Nov14.222140.22741@iwarp.intel.com>
Date: 14 Nov 90 22:21:40 GMT
References: <27962@sequoia.execu.com>
Sender: news@iwarp.intel.com
Reply-To: merlyn@iwarp.intel.com (Randal Schwartz)
Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
Lines: 54
In-Reply-To: painter@sequoia.execu.com (Tom Painter)

In article <27962@sequoia.execu.com>, painter@sequoia (Tom Painter) writes:
| In the following script, I trying to strip all lines before the first
| blankline from stdin.  In that vein, I set a flag ($header) to "Y"
| and change it to "N" after it hits the blank line.  So far it works.
| However, when I return to the top of the while loop, $header has been changed 
| back to "Y".  The "N" should last for the rest the time, I never want it
| changed back. 
[...]
| #! /usr/bin/perl
| 
| $header = "Y";
| 
| while (<>) {
| print $header;
| 	if ($header = "Y"){ 
| 		if (/^$/){
| 			$header = "N";
| 		}
| 		next;
| 	}
| 	if (grep(/SOME STRING/,$_)){
| 		printf "\n";
| 	}
| print;
| }

The line beginning "if ($header ..." needs a "eq", not a "=".  Also,
I've never seen the grep operator used for a single entry (not even in
a JAPH :-).  Simply /SOME STRING/ would do it.

Here's something closer to what you want:

#!/usr/bin/perl

while (<>) {
	$header = /^$/..eof ? "N" : "Y";
	print $header;
	print "\f\n" if /SOME STRING/;
	print;
}

Some explanation on that first line: the construct "/^$/..eof" is true
from the first blank line to the end of the file.  This is a handy
idiom, duplicating your logic.  More often, you'll see something like
"1../^$/", which is true from the first line of the file to the first
blank line (not quite the same thing... think of the value *at* the
blank line).

print "Just another Perl hacker,"
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
| merlyn@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
\=Cute Quote: "Intel put the 'backward' in 'backward compatible'..."=========/