Question

I am writing a perl program to extract lines that are in between the two patterns i am matching. for example the below text file has 6 lines. I am matching load balancer and end. I want to get the 4 lines that are in between.

**load balancer** 
new 
old
good
bad
**end**

My question is how do you extract lines in between load balancer and end into an array. Any help is greatly appreciated.

Answer 1

You can use the flip-flop operator.

Additionally, you can also use the return value of the flipflop to filter out the boundary lines. The return value is a sequence number (starting with 1) and the last number has the string E0 appended to it.

# Define the marker regexes separately, cuz they're ugly and it's easier
# to read them outside the logic of the loop.
my $start_marker = qr{^ \s* \*\*load \s balancer\*\* \s* $}x;
my $end_marker   = qr{^ \s* \*\*end\*\* \s* $}x;

while( <DATA> ) {
    # False until the first regex is true.
    # Then it's true until the second regex is true.
    next unless my $range = /$start_marker/ .. /$end_marker/;

    # Flip-flop likes to work with $_, but it's bad form to
    # continue to use $_
    my $line = $_;

    print $line if $range !~ /^1$|E/;
}

__END__
foo
bar
**load balancer** 
new 
old
good
bad
**end**
baz
biff

Outputs:

new 
old
good
bad