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Useful Perl Scripts With Regular Expressions
By Matthew Drouin - 2003-12-18 Page:  1 2 3 4 5 6

Replace On A Single File

Here we will hard code our script to edit a single file for certain words. You could set the script up to prompt the user for the file but I figured that was over kill since we would probably have to go in and make some minor changes to the script anyway. If you want the script to prompt you can use the code below though.

my $dir;
"Please enter dir name: ";
chomp ( $dir = <STDIN> );


The code above prints out Please enter dir name: and then we use chomp, which we will discuss later, to remove the linefeed and or newline that comes in when the user hits enter.

The code below will parse a file that contains a <body ... > tag and we want to remove all the attributes in the body tag because we are starting to use cascading style sheets (CSS) and we no longer want there to be any attributes in the body tag since we will define all of the attributes in our .css file. Our file will start out with <body bgcolor="green"> and we will end up with <body>.

It would probably not make much sense to use this script to edit just one file because it would be faster to open the HTML document and make the change manually than it would be to edit this script and then run it. We will be building upon this script so it is not a waste of time.


$filename = "/home/directory/file.txt";
open ( FILE, $filename) or die "Cannot open file: $!";

while (
$line = <FILE> ) {
# i is case insensative
    # ([^>]*) match zero or more characters but not '>'
$line =~ s/<body([^>]*)>/<body>/i;
push(@outLines, $line);

close FILE;

open ( OUTFILE, ">$filename" );
print (
OUTFILE @outLines );
close ( OUTFILE );


You will notice above that we open the file once to read it and then we open the file again to write to it. The reason I did this is because it is possible you would actually output to a different file than the original and if that is the case then the code already exists for you to do so easier than if I had only done this process with one open file statement.

In the above code you will also notice the regular expression ([^>]*) which stops the regular expression from doing a maximum munch; i.e. it tells the regular expression to stop at the first greater than sign instead of stopping at the last greater than sign in the file. If this were not here, and you can feel free to give this a try, the regular expression code would actually take everything from the body tag all the way to the last greater sign removing everything, in a well formatted HTML document, from the body tag to the closing html tag and replace it will just a simple <body> tag.

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Copyright 2003-2004 Matthew Drouin. All rights reserved.

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