Well, I needed to add few extensions to the browser and i ended with this...
It generates a working chrome extension with only a context menu that acts as 'Search with <your search engine>'.

You'll call the script with only 2 args: a_description and a partial URL
as in extgen.pl Cpan_search http://search.cpan.org/search?query=

Then you point chrome to chrome://extensions/, check Developer Mode and choose Load an unpacked extension and browse to early created folder containing the extension.

Here is the code:

#!/usr/bin/perl
use strict;
use warnings;

my $folder = $ARGV[0];
my $url  = $ARGV[1];

(my $descr = $folder) =~ s/_+/ /g;
my $longname = 'Perl genarated extension - '.$descr;

mkdir $folder or die "Cannot create $folder: $!";
chdir $folder or die "Cannot enter $folder: $!";
# the manifest
open MANIF, '>', 'manifest.json' or die "Cannot open a file to write i
+n: $!";
my $manifest = '{
   "manifest_version": 2,
   "description": "'.$descr.'",
   "background": {
    "scripts": ["background.js"]},
   "name": "'.$longname.'",
   "permissions": [ "contextMenus", "tabs" ],
   "version": "1.0"
}';
print MANIF $manifest;
close MANIF;
# the jscript
open JSCRIPT, '>', 'background.js' or die "Cannot open a file to write
+ in: $!";
my $background ='function customfunc(info)
{
 var searchstring = info.selectionText;
 chrome.tabs.create({url: "'.$url.'" + searchstring})
}
chrome.contextMenus.create({title: "'.$descr.'", contexts:["selection"
+], onclick: customfunc});';
print JSCRIPT $background;
close JSCRIPT;
[download]

UPDATE 2023 see a working manifest v3 working code needed since 2023: Re: [OT] migrating from scripts to service_worker in js perl generated extensions for chrome -- solved

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