Perl Regular Expression to insert/substitute in a string at specific places - regex

Question

Given a url the following regular expression is able insert/substitute in words at certain points in the urls.
Code:
#!/usr/bin/perl
use strict;
use warnings;
#use diagnostics;
my #insert_words = qw/HELLO GOODBYE/;
my $word = 0;
my $match;
while (<DATA>) {
chomp;
foreach my $word (#insert_words)
{
my $repeat = 1;
while ((my $match=$_) =~ s|(?<![/])(?:[/](?![/])[^/]*){$repeat}[^/]*\K|$word|)
{
print "$match\n";
$repeat++;
}
print "\n";
}
}
__DATA__
http://www.stackoverflow.com/dog/cat/rabbit/
http://www.superuser.co.uk/dog/cat/rabbit/hamster/
10.15.16.17/dog/cat/rabbit/
The output given (for the first example url in __DATA__ with the HELLO word):
http://www.stackoverflow.com/dogHELLO/cat/rabbit/
http://www.stackoverflow.com/dog/catHELLO/rabbit/
http://www.stackoverflow.com/dog/cat/rabbitHELLO/
http://www.stackoverflow.com/dog/cat/rabbit/HELLO
Where I am now stuck:
I would now like to alter the regular expression so that the output will look like what is shown below:
http://www.stackoverflow.com/dogHELLO/cat/rabbit/
http://www.stackoverflow.com/dog/catHELLO/rabbit/
http://www.stackoverflow.com/dog/cat/rabbitHELLO/
http://www.stackoverflow.com/dog/cat/rabbit/HELLO
#above is what it already does at the moment
#below is what i also want it to be able to do as well
http://www.stackoverflow.com/HELLOdog/cat/rabbit/ #<-puts the word at the start of the string
http://www.stackoverflow.com/dog/HELLOcat/rabbit/
http://www.stackoverflow.com/dog/cat/HELLOrabbit/
http://www.stackoverflow.com/dog/cat/rabbit/HELLO
http://www.stackoverflow.com/HELLO/cat/rabbit/ #<- now also replaces the string with the word
http://www.stackoverflow.com/dog/HELLO/rabbit/
http://www.stackoverflow.com/dog/cat/HELLO/
http://www.stackoverflow.com/dog/cat/rabbit/HELLO
But I am having trouble getting it to automatically do this within the one regular expression.
Any help with this matter would be highly appreciated, many thanks

Answer 1

One solution:
use strict;
use warnings;
use URI qw( );
my #insert_words = qw( HELLO );
while (<DATA>) {
chomp;
my $url = URI->new($_);
my $path = $url->path();
for (#insert_words) {
# Use package vars to communicate with /(?{})/ blocks.
local our $insert_word = $_;
local our #paths;
$path =~ m{
^(.*/)([^/]*)((?:/.*)?)\z
(?{
push #paths, "$1$insert_word$2$3";
if (length($2)) {
push #paths, "$1$insert_word$3";
push #paths, "$1$2$insert_word$3";
}
})
(?!)
}x;
for (#paths) {
$url->path($_);
print "$url\n";
}
}
}
__DATA__
http://www.stackoverflow.com/dog/cat/rabbit/
http://www.superuser.co.uk/dog/cat/rabbit/hamster/
http://10.15.16.17/dog/cat/rabbit/

Answer 2

Without crazy regexes:
use strict;
use warnings;
use URI qw( );
my #insert_words = qw( HELLO );
while (<DATA>) {
chomp;
my $url = URI->new($_);
my $path = $url->path();
for my $insert_word (#insert_words) {
my #parts = $path =~ m{/([^/]*)}g;
my #paths;
for my $part_idx (0..$#parts) {
my $orig_part = $parts[$part_idx];
local $parts[$part_idx];
{
$parts[$part_idx] = $insert_word . $orig_part;
push #paths, join '', map "/$_", #parts;
}
if (length($orig_part)) {
{
$parts[$part_idx] = $insert_word;
push #paths, join '', map "/$_", #parts;
}
{
$parts[$part_idx] = $orig_part . $insert_word;
push #paths, join '', map "/$_", #parts;
}
}
}
for (#paths) {
$url->path($_);
print "$url\n";
}
}
}
__DATA__
http://www.stackoverflow.com/dog/cat/rabbit/
http://www.superuser.co.uk/dog/cat/rabbit/hamster/
http://10.15.16.17/dog/cat/rabbit/

Answer 3

one more solution:
#!/usr/bin/perl
use strict;
use warnings;
my #insert_words = qw/HELLO GOODBYE/;
while (<DATA>) {
chomp;
/(?<![\/])(?:[\/](?![\/])[^\/]*)/p;
my $begin_part = ${^PREMATCH};
my $tail = ${^MATCH} . ${^POSTMATCH};
my #tail_chunks = split /\//, $tail;
foreach my $word (#insert_words) {
for my $index (1..$#tail_chunks) {
my #new_tail = #tail_chunks;
$new_tail[$index] = $word . $tail_chunks[$index];
my $str = $begin_part . join "/", #new_tail;
print $str, "\n";
$new_tail[$index] = $tail_chunks[$index] . $word;
$str = $begin_part . join "/", #new_tail;
print $str, "\n";
}
print "\n";
}
}
__DATA__
http://www.stackoverflow.com/dog/cat/rabbit/
http://www.superuser.co.uk/dog/cat/rabbit/hamster/
10.15.16.17/dog/cat/rabbit/