assuming you would want to process all log files in a directory and extract line lines with keyword ..

$keyword = "your keyword here";

open hanw,"<" , "output.txt" or die "could not open output file $!";

opendir(hand,$dirpath);  #replace with your DIR
    @files = readdir(hand);
    closedir(hand);

    foreach(@files){
        if(/\.log$/i) {                                               
+      #if the filename has .log at the end
            push(@logfiles,$_);  
        }
    }

$nooffiles = @logfiles;
$fileindex=0;
while ($fileindex <$nooffiles )
{
open hanr ,">", "$logfiles[$fileindex]" or die "could not open logfile
+ .. $!";
while (<hanr>) {
if ($_ =~ /$keyword/ ) {
print hanw ;
#last;  --if it will occur only once
}
} 
close hanr;
$fileindex++;
}

close hanw;
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if you are sure it will occur inside a block then use the code block using flip flop operator as suggested above

 if (/$start/i .. /$end/i)
# where start and end are your start and end keywords
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