variable reference problem

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

I am writing a script to parse log. I am reading each line from the log and if some condition satisfies I want store that line to some buffer variable and I want to use that buffer later. but the problem is when I print buffer later, the value is changed to the last line. here is the snippet.

while (<$fhlog>)
{
my $line = $_;
my $bufferline;
if ($line =~ /Finished (.*)\. Wrote (\d+) new, (\d+) duplicates, (\d+)
+ archived/)
 {
  &storeAdapterDetails($1, $2, $3, $4, $fhresult);
  next;
 }
 if ($line =~ /ERROR/)
 {
  $bufferline = '$line';
  next;
 }
 if ($line =~ /.*Exception:/)
 {
  print "Found adapter: ".$bufferline;            
  $flag = 1;
 }
[download]

20080916 Janitored by Corion: Added formatting, code tags, as per Writeup Formatting Tips

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Re: variable reference problem by bobf (Monsignor) on Sep 11, 2008 at 03:19 UTC
Thanks for providing your code, but it's very hard to read without formatting. Please use 'code' tags as described in Writeup Formatting Tips, as follows: `while (<$fhlog>) { my $line = $_; my $bufferline; if ($line =~ /Finished (.)\. Wrote (\d+) new, (\d+) duplicates, ( +\d+) archived/) { &storeAdapterDetails($1, $2, $3, $4, $fhresult); next; } if ($line =~ /ERROR/) { $bufferline = '$line'; next; } if ($line =~ /.Exception:/) { print "Found adapter: ".$bufferline; $flag = 1; }` [download] Some comments: `$bufferline` is declared inside the while loop, so any values assigned to it in one iteration will not be available in subsequent iterations (or after the loop is complete). Calling `storeAdapterDetails` with a leading '&' has consequences (see perlsub). Did you use it intentionally? If not, you may want to remove it to avoid potential bugs in the future. `$fhresult` is not declared in your example; I assume it is set prior to the loop Single quotes do not interpolate, so `$bufferline` is getting set to the literal string `'$line'`. You probably want `$bufferline = $line;` instead. Using 'next' after assigning to `$bufferline` prevents evaluation of the following if statement, so the print statement containing `$bufferline` will not be executed. Furthermore, when that statement is executed, `$bufferline` will be uninitialized. `$flag` is not declared in the loop, so I assume it was declared previously Using sequential 'if' statements implies (to me) that it is possible for more than one condition to apply during each iteration. If that is not the case (based on the use of 'next'), 'elsif' may convey more meaning to anyone reading the code. There is nothing wrong with `while( <$fhlog> ) { my $line = $_; ... }`, but I would write that as `while( my $line = <$fhlog> ) { ... }` Hope this helps	[reply] [d/l] [select]
Re^2: variable reference problem by priyankgandhi (Novice) on Sep 12, 2008 at 08:34 UTC
Hi thanks for your help. You cleared many of my doubts. Re: 2nd point I dont know any difference in calling subroutine with '&' or without '&'. Can you explain me? Thanks for the Writing Formatting link. I will follow the standards.	[reply]
Re^3: variable reference problem by ikegami (Patriarch) on Sep 12, 2008 at 09:42 UTC
"`&`" causes Perl to ignore the sub's prototype. Some people use "`&`" to indicate a user sub, since it can only be used on subs, not on builtin functions. But I think that's a bad idea since "`&`" is not just decorative. You might be interested in reading (tye)Re: A question of style.	[reply] [d/l] [select]
Re: variable reference problem by ikegami (Patriarch) on Sep 11, 2008 at 00:02 UTC
Your buffer is declared inside the loop, so the variable is cleared after every loop pass, so I find it hard to believe is has any value later.	[reply]