If your parameter is always an URI, you could use the CPAN Modules URI and File::Basename. 
use File::Basename;
use URI::Split qw(uri_split uri_join);

my @uri = uri_split('https://www.domain.com/aaa/bbb/file.zip');

$uri[3]    = 'file='.basename($uri[2]);
$uri[2]    = 'file_publish';

my $uri = uri_join(@uri);

print $uri."\n";

[download]

In reply to Re: Define regex substitution $1,$2,... from a string by ablanke
in thread Define regex substitution $1,$2,... from a string by sylph001

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