How can I emulate 'grep -B' functionality in Perl?

Question

I have been searching for a solution that allows me to search the lines of an array, and if a string match is made, push that line and the 2 previous lines into an array. It

Answer 1

You are mixing up the grep program /bin/grep with the perl function named grep (perldoc -f grep). While the former takes additional parameters, like -B, the latter does not.

Answer 2

A basic version of your subroutine. I assume you wanted to return the list when done with it. Untested.

sub ipsearch {
    my $ip = shift;
    my @IPVSCONFIG = (); # no matches should be empty list, not undef
    my @buffer = ()      # to avoid undef warnings
    for (@RAWDATA) {
        push @buffer, $_;
        shift @buffer if @buffer > 3;
        if (/\W+virtual\s$ip\s/) {
            push @IPVSCONFIG, @buffer;
            @buffer = ();
        }
    }
    return @IPVSCONFIG;
}

Answer 3

The trick is to identify the lines where the match occurs, then identify the relevant indices around:

Get the matched indices:

my @matchedIndices = grep { $RAWDATA[$_] =~ /\W+virtual\s$ip\s/ } 2 .. $#RAWDATA;

Get the indices around:

my @wantedIndices  = map { ( $_-2 .. $_ ) } @matchedIndices;

And take an array slice:

my @IPVSCONFIG = @RAWDATA[ @wantedIndices ];

Putting it altogether in a Schwartzian transform:

my @IPVCONFIG = map  { @RAWDATA[$_-2..$_] }
                grep { $RAWDATA[$_] =~ /\W+virtual\s$ip\s/ }
                2 .. $#RAWDATA ;

Definitely a much busier solution than the traditional command-line grep -B 2!