if you want to print the last 10 lines in order of highest line number to lowest line number after "something special" is found change this line:
print "$_\n" for @queue;
to:
print "$_\n" for (reverse @queue);
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Question
perl: print last 10 lines
I am searching through a file line by line:
foreach $line (<FILE>)
{
if($line eq "something special")
{
here I want to print out the last 10 lines before $line
}
}
I'm new to perl, so I wanted to check with the experts. My guess on the best way to implement this is to use a queue of some kind. Each time a line is read, add it to the queue. When the queue is larger than 10 items, dequeue a line when a new one is added.
Is that the best way to accomplish this? The file I will be reading has tens of thousands of lines, so I want to do this in the most efficient way possible.
Thanks.
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by: Perl_DiverPosted on 2006-06-08 at 11:18:03ID: 16863838
untested code, it might need some tweaking to get exaclty what you want:
my @queue = ();
foreach $line (<FILE>) {
chomp($line); #<-- you may not need to chomp $line
if ($line eq "something special") {
# here I want to print out the last 10 lines before $line
print "$_\n" for @queue;
}
push @queue,$line; #adds current line to end of @queue
shift @queue if (@queue > 10); #removes the first line from @queue if more than 10 lines are in @queue
}
Tie::File is also an option, but I am not sure if it would be any more efficient than the above scenario.