Perl script to replace a line after finding a previous line

Mark1986 · 02-28-2011, 01:32 AM

Hi all,

At the moment I have a flat file which is being used by a few people. I want a script to remotely change the file, so I can start logging who is doing what.

At this point here is one requirement I am trying to develop. We have text blocks who pretty much look like this:

---------------------- C001

$$var1=Source
$$var2=Target
$$var3=2

---------------------- C006

$$var1=Source
$$var2=Target
$$var3=3

In this text block I first want to find C001 and afterwards change $var3. Thing is, I don't want to change all $var3's.

This is my code so far;

Code:

	open(PARAM, "<be_cycle3b.prm") or die ("Kan parameter bestand niet openen.");

	my @dat_param = <PARAM>;

	foreach my $regel (@dat_param){

		if( $regel =~ /^-+ +$workflow/g ){

			print $regel;

			foreach (my $regel_n = @dat_param) {

				print " \n regel_n: " , $regel_n  , " \n ";

				if( $regel_n =~ /^$param/ ){
					
					print " foreach regel_n: ",$param;

					print $regel_n;
				}
			}


		}

	}

	close(PARAM);

I have not come to the point of changing $$var3. Even trying to read the line with $var3 is not possible yet.

Here are the used variables:

$workflow (C001 as in example given)

$param = $$var3

I hope this is somewhat clear. I try to find $param for the right $workflow and change that. Can you help me to find $$var3 and change that?

Much appreciated.

kris_kiil · 02-28-2011, 05:09 PM

My recommendation is to use a state structure, since this makes it fairly simple to see what is going on.

Code:

	open(PARAM, "<be_cycle3b.prm") or die ("Kan parameter bestand niet openen.");
        
	my @dat_param = <PARAM>;
        my $state = 0;
	foreach my $regel (@dat_param){
		if( $regel =~ m/^-+/ ){
                        if($regel =~ m/$workflow/){
                                #You found the right section
                                $state = 1;
                        }
                        else{
                                #You are in a wrong section
                                $state = 0;
			}
                }
                if($state == 1 and $regel =~ m/^$param/){
                        # You have now read the right line,
                        # so do something useful below.
			print "$regel";
		}
        }

This way you don't end up processing the wrong lines.

As for how to change $var3, just remember that, if $var = 'a' you can access $a as $$var, but read the perlreftut and/or perlref manpages for the complete story.

Good luck