How to use perl to replace text between two specific lines

Question

Hi I have a html called 1.html file like this

<div class="t_l"></div>
 <some> 
   lines
     of
 codes
 </some>
<div class="t_r"></div>

I want to replace the content of that div to another one, which stored in the file called "banner". banner file is

<other> 
   lines
     of some
 codes
</other>

So what I want to get is:

<div class="t_l"></div>
 <other> 
   lines
     of some
 codes
 </other>
<div class="t_r"></div>

What I come up with using perl is something like this:

# Slurp file 1.html into a single string
open(FILE,"1.html") or die "Can't open file: $!";
undef $/;
my $file = <FILE>;
open(BANNER,"banner") or die "Can't open file: $!";
undef $/;
my $banner = <BANNER>;
close BANNER;

# Set strings to find and insert
my $first_line = '<div class="t_l"></div>';
my $second_line = '<div class="t_r"></div>';

$file =~ s/$first_line\n.+?\n$second_line#s/$first_line\n$banner\n$second_line/;

close FILE;

# Write output to output.txt
open(OUTPUT,">1new.html") or die "Can't open file: $!";
print OUTPUT $file;
close OUTPUT;

The above code cannot work. Any suggestions?

You should use one of the perl HTML parser modules, like HTML::TokeParser, for example. — David
– David, Commented Sep 6, 2012 at 21:50
You really don't want to parse HTML with regular expressions. That way lies madness :-/ — Dave Cross
– Dave Cross, Commented Sep 7, 2012 at 9:42

mob · Accepted Answer · 2012-09-06 21:51:01Z

2

You're almost there.

The normal regex behavior of . is to match any character except a newline. .+? in your regex doesn't work for you because there are more newline characters between $first_line and $second_line.

Using the /s modifier tells Perl to let . match newline characters, too.

(You also have an extraneous "#s" in your expression)

So a working substitution is:

$file =~ s/$first_line\n.+?\n$second_line/$first_line\n$banner\n$second_line/s;

answered Sep 6, 2012 at 21:51

mob

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Ωmega · Accepted Answer · 2012-09-06 22:45:31Z

1

Go with

$file =~ s/($first_line\n)[^\n]+(\n$second_line)/$1$banner$2/;

or

$file =~ s/(?<=$first_line\n)[^\n]+(?=\n$second_line)/$banner/;

answered Sep 6, 2012 at 22:45

Ωmega

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