modify lines between two tags in perl - perl

Question

I need some help with replaceing lines between two tages in perl. I have a file in which I want to modify lines between two tags:
some lines
some lines
tag1
ABC somelines
NOP
NOP
ABC somelines
NOP
NOP
ABC somelines
tag2
As you can see, I have two tags, tag1 and tag2 and basically, I want to replace all instances of ABC with NOP between tag1 and tag2. Here is the relevant portion of code but it doesn't replace. Can anyone please help..?
my $fh;
my $cur_file = "file_name";
my #lines = ();
open($fh, '<', "$cur_file") or die "Can't open the file for reading $!";
print "Before while\n";
while(<$fh>)
{
print "inside while\n";
my $line = $_;
if($line =~ /^tag1/)
{
print "inside range check\n";
$line = s/ABC/NOP/;
push(#lines, $line);
}
else
{
push(#lines, $line);
}
}
close($fh);
open ($fh, '>', "$cur_file") or die "Can't open file for wrinting\n";
print $fh #lines;
close($fh);

Answer 1

Consider a one-liner using the Flip-Flop operator.
perl -i -pe 's/ABC/NOP/ if /^tag1/ .. /^tag2/' file

Answer 2

Use $INPLACE_EDIT in conjunction with the range operator ..
use strict;
use warnings;
local $^I = '.bak';
local #ARGV = $cur_file;
while (<>) {
if (/^tag1/ .. /^tag2/) {
s/ABC/NOP/;
}
print;
}
unlink "$cur_file$^I"; #delete backup;
For alternative ways to edit a file, check out: perlfaq5

Answer 3

Your line which says $line = s/ABC/NOP/; is incorrect, you need =~ there.
#!/usr/bin/perl
use strict;
use warnings;
my $tag1 = 0;
my $tag2 = 0;
while(my $line = <DATA>){
if ($line =~ /^tag1/){
$tag1 = 1; #Set the flag for tag1
}
if ($line =~ /^tag2/){
$tag2 = 1; #Set the flag for tag2
}
if($tag1 == 1 && $tag2 == 0){
$line =~ s/ABC/NOP/;
}
print $line;
}
Demo