I think it's OK to do that once. If a determined human is allowed to do it by hand, standalone is no different. You hadn't mentioned periodically though -- for that, there's standards and rules.

Your program is nothing more or less than an ordinary, ubiquitous web-spider. Does wordpress.org militate against them? Check http://wordpress.org/robots.txt :

Code:

User-agent: *
Disallow: /search
Disallow: /support/search.php
Disallow: /extend/plugins/search.php
Disallow: /plugins/search.php
Disallow: /extend/themes/search.php
Disallow: /themes/search.php
Disallow: /support/rss
Disallow: /archive/

They have places spiders clearly aren't supposed to go, mostly their search functions (probably slow and expensive). Their flat listing of popular plugins is not excluded -- wget would have flat-out refused to work if it was, it's polite like that.

They could have also refused wget's very well-known user agent value and haven't. They don't militate against referer values either, and haven't obfuscated anything with logins, javscript, or cookie nonsense. They don't even have advertising to be annoyed about humans never seeing. As far as I'm concerned it's in the clear. You are inside the marked areas, not doing anything obviously wrong, on a site with no ads or interactive restrictions. If you don't impact their performance and don't do anything suspicious, why would they care? Downloading information is what their web site is for.

The rules for polite spiders, as I see them:

A more polite spider which flags itself, limits impact and bandwidth, and obeys robots.txt:

Code:

wget -U popular-checker --wait=1 --limit-rate=50K --header="Accept-Encoding: gzip" \
        "https://wordpress.org/plugins/browse/popular/"  https://wordpress.org/plugins/browse/popular/page/{2..34}/ -O - 2>/dev/null |
        gunzip | 
        grep -o "wordpress.org/plugins/[^/\"']*" |
        awk '{ sub(/wordpress[.]org[/]plugins[/]/, ""); } $1 && !/[.]php$/' | sort -u > plugins.txt